TIM SIM for Italy

First of all make sure your phone is unlocked otherwise you won’t be able to use another carrier. If your phone is fully paid, then it can be unlocked if it’s not unlocked already.
You will lose absolutely nothing in terms of apps, email, etc. your phone with the Italian SIM will work exactly the same as with your American SIM.
The only issue is that since your American SIM card is no longer inside the phone (since now you replaced it with the Italian one), you will not be able to receive calls to your American number or messages. So make sure you tell your American relatives how to reach you (give them your Italian number or email). The calls to your American number will go to voicemail. You can check them by reinserting the American SIM card, but calling your America voicemail will count as a call therefore you may be charged for roaming fees by your American carrier.

Be aware that Tim's plan for tourists does not include texts and it can't be renovated after the first 30 days. You could keep the Italian number, but you should either buy a new plan or top up and pay as you go per giga/text/minute of talking time.

I hope Apple solved the problem, but a couple of years ago, some US iPhones sent texts in background to an US number when customers installed the new Italian SIM. It can be a problem, since texts are not included in the Tourists' plan you could go negative and lock the TIM SIM.

We had a Tim Sim in Italy 2019. Phone worked well and plenty of data but you shouldn't text. Your email account should still work on hotel etc. WiFi (not the mobile phone connection). It might be slow to access but you should be able to get your emails.

I've use TIM for longer trips to Italy. Having an Italian phone number is way cheaper than using your US number.
Here are some ways to make it work.

1. Get all your friends/relatives on WhatsApp BEFORE you leave. Use WhatsApp to call/text them in the U.S.
2. Since you won't be calling the US from your new Italian number (you'll be using WhatApp) and not making lots of local Italian calls, you don't need an expensive complicated plan. Get at most a 15G plan for data. (use the data at cafes or your lodging to do most of your sending/writing, etc). I used GPS, Google maps, took pics and sent them out sometimes and in one month only used 2G. In the 3 months of having my TIM card I never came close to using the 10G /month I paid for. DON'T LET THEM SELL YOU A HIGH DATA PLAN! There is internet at your hotel, bars, cafes, etc. If there is internet you can use that and not your TIM plan data.

AT THE TIM STORE
1. have them put the new SIM card in for you. Put your SIM card in a small case. (do it mindfully...you may be tired so make sure you know where you put your U.S. SIM card!)
2. Have them install the TIM APP on your phone. It's great for checking data, etc.
3. Have them test the phone to make sure it works.
4. Send a WhatsApp to someone to make sure it works before you leave.

QUESTIONS TO ASK THEM
1. are the prompts in English? If not, have them change the prompts to English.
2. how do I check my balance? (have them show you. It will be on the TIM app, but they'll walk you through it).
3. Confirm the fees for domestic calls and domestic texts
4. How do I buy more time if needed?

If you arrive in Rome FCO.
Last time I bought my SIM card there, the TIM store was near Hertz and Avis and the information desk, before you got to baggage pick-up.
I like having my Italian number BEFORE I leave the airport. Then I can quickly WhatsApp my family/friends to let them know we arrived safely.
Hope this helps!

What a wonderfully helpful, thorough post, CaliforniaCuore! It is super nice that you took the time to put that comprehensive post together. Wish we could pin it !

Thank you, thank you, thank you. Each of you contributed great info. This helps us so much. Right now we R/T in and out of Bologna-subject to change as all travel plans are right now. My next post may well be about WhatsApp!
I would hope that Apple has fixed the issue. Will check into that too.
Our phones are unlocked, but we will confirm that before departure.
My small amount of research suggests NOT to purchase a SIM at the airport, but that could have changed or been more relevant to Venice (our original entrance). I understand that whomever we get our cards from has to initiate because of the codice fiscale. I will put californiacuores’ post into my notes for future reference! Fabulous.
10GB sounds good, especially if each of us has that much. Sure we won’t use it but I would rather have more than not enough. Open for discussion as 5GB could certainly be plenty. My husband has a far better grip on what amount we use each month. We won’t let them sell us too much!
Grazie ancora.

I should also note we will have an iPad with us that does not have cellular, so possibly its’ use is for research when we are at our lodging and we use our phones when out and about. I prefer to look info up on it anyway as it’s much easier to use. This may well be the answer to far less GB of data for the phones.

I understand that whomever we get our cards from has to initiate because of the codice fiscale.

I am afraid I can't understand this sentence, but the Italian Fiscal Code is just your name, surname, place and date of birth summarized into an alphanumeric code using a public algorithm. In other words, you can get yours here: https://www.codicefiscale.com/

"LUOGO DI NASCITA" means Place of Birth, the Italian translation of United States of etc. etc. is "Stati Uniti d'America"

Be aware of the difference between re-sellers and Tim's brand stores.

Dario-thank you. Codice fiscale sounds very official like a tax registration or something. It was in an article I read from an American with dual citizenship who lives in Italy. One less thing to be concerned about!

Codice fiscale done and saved! Thank you Dario.

And no!! Didn’t save to my notes-error produced. Will try again. And I tried again. It generates a number but when I share it to notes, I get the “Ops! Qualcosa e andato storto.” So, it either doesn’t want the info to be shared to another place or the system is acting up. Maybe I’ll try again tomorrow.

a lot of great information has been posted already so i'll just add a specific issue i had while traveling in italy last summer. nothing to do with the sim card but with my boa travel rewards credit card. whenever i tried to pay for something online with the card, e.g. trainitalia or intercity bus tickets, i got an email from boa requiring me to enter a code to validate the purchase. the problem was that the code was sent via text to my verizon number. i couldn't figure out how to have access to the text from my now 'converted' tim phone. mind you, it was not a tim problem but something i should have thought of and set up a different method of verifying purchases with boa before leaving. i probably could have done it from italy but felt like a hassle not worth dealing with. fyi, i used both a tim and a vodaphone sim without any issues in my android phone. my suggestion is to clarify with your credit card company/bank before leaving the usa.

If your credit card, bank or ? uses 2 factor authentication (2FA), have the code sent to an accessible email (gmail is good). For BofA, you have to tell them you can't use your phone for 2FA, must use an email acct. Be persistent. Sometimes that means clicking on "have trouble receiving text?" or similar message. You MUST tell the card company where & when you are traveling. And provide an alternate number of a family member if possible. Nowadays it is sometimes harder to pay with a card than when travelers checks were the 'thing'. I wonder if covid has made some countries accept cash again.

Oh my. Thank you for this info. Hadn’t thought about that at all. Will add to the list of “things to do” before leaving the country. There must be a way to change the phone number for those accounts as this won’t be new to BoA and others.

Make sure you include your First and Middle name to generate your codice fiscale, if your passport has a middle name. The result will be different if you don't.
It is a good idea to get your American contacts on WhatsApp and to get them familiar with it. Many Americans are not familiar with it, unless they travel abroad. You can also make phone calls using WhatsApp, not just texts, use it to make calls to your US contacts that have WhatsApp. If you have Italian contacts you can call their mobile phone using WhatsApp too. Use Whatsapp to make calls to any mobile phone, US or Italian. It's free. No need to use voice minutes.

If you have a recent iPhone--11, 12, 13 and some Xs, you can convert your US physical SIM to an e-SIM that's stored somewhere in the phone's memory. That way, when you buy the Italian SIM, you won't have to remove the US SIM. You can switch between the two accounts easily if, for example, you want to see if you've got voicemail on your US number. Just keep in mind that when you do that, you'll trigger the US carrier's charge of $10 or so a day JUST FOR THAT DAY. If it's work-related, you can probably expense that. And Roberto's right--get used to WhatsApp; most Europeans use it. Think of it as an Apple Messages app that works across platforms, for those who've got Androids.

We get Verizon International plan for one phone fir medical and family emergencies and a SIM card gor the other phone. We have used TIM among others. This plan works well for us.

Roberto da Firenze
I finally just typed the Codice into my notes. There didn’t appear to be a need for middle names, however, if we find we need them once we arrive for proper use (both of us have middle names on our passports), we’ll do it then. Thank you.

apaonita
We do have newer phones that possibly will support the e-sim. Think it’s a trip to the Apple Store for that info/addition. Thank you.

Middle names (or initials) is a very much North American thing, rare on this side of the pond. Rarely that anybody asks for it or checks it.