Getting a SIM card in Rome for Android phones

The major mobile providers are: TIM, Vodafone, Wind, 3 (in order of subscribers).
There are phone stores everywhere, including the train station.
Prices vary depending on the amount of data (Gigabytes) you need. But 25 euro, including the cost of the SIM card, will get you at least 1Gb and plenty of local minutes and SMS text messages, plus 5 euro balance for extra costs (like calls overseas or foreign roaming).
Not sure what you mean by data in English, the data comes in bytes, not English. When you access the Voice Mail, the voice commands will be in Italian however, and I don't know if you can get around that. Also when you receive automatic SMS notifications (for example the confirmation of the amount of money you reload, if you reload more money) they will be in Italian.
Calls made overseas may not be included in you plan, therefore they will be deducted from you balance embedded in the SIM card. If your balance goes negative, you need to reload more money in tha card, or the phone will stop working. You can reload money at any Tobacconist shop or phone authorized dealer.

Thank you for the advice. Much appreciated.

"When you access the Voice Mail, the voice commands will be in Italian however, and I don't know if you can get around that. Also when you receive automatic SMS notifications (for example the amount of money you reload, if you reload more money, will be in Italian."

When I got a TIM SIM in 2014, I was able to get the voice prompts to be changed to English, but the texts (SMS) from TIM were indeed still in Italian. The important ones, of how much credit I had left, were easy to decipher; the ones telling me about their latest offers (for music downloads and such) were a bit harder, but I wasn't interested in these anyway.

I had a dumbphone and so didn't need data; I got the TIM Simple Start plan. My friend had a smartphone, and used the TIM Welcome package and was happy with it. For €30, you get a SIM, 200 minutes of calls (either domestic or international), 2GB of data (4G speed where available) and €5 of credit for texts or more calls. For only 7 days, that will probably be all you need, but if you use any part of it up, you can then buy another kind of package (the TIM Welcome is not renewable). Details are here: http://www.tim.it/estero/dall-italia/tim-welcome-uk

Roberto has indicated that the other companies have similar offers (I haven't investigated these).

When you get your account set up in the store, before you leave, make sure they change the voice prompts to English, and make sure they show you how to check your remaining minutes and data.

Also check your carrier. T-Mobile has good plans that allow you to use your same phone and number overseas.

Thanks for all the replies. Are TIM or Vodafone SIM sold at the Rome Airport?

When we arrived in Milan we went to the Vodaphone store near the Duomo and then salespeople were very helpful and English speaking. Although we were worried about doing this, we have been pleased with the plan of about 25 Euros for 30 days per iPhone. With this we each got 300 minutes talk time which included calling the U.S. and 2 GB of data and plenty of texting. Since then I have noticed Vodaphone at most large train stations so I am sure they are at all large airports. We both have iPhone 6 and there was no problem.

In retrieving messages on an iPhone, it is the same as in the U.S. - I haven't noticed any issues with Italian commands. All is the same just the carrier is different. It is great having an Italian number so our AirBNB hosts etc. can reach us if needed.

The store did submit our passport information for anti-terrorism review and said within two hours we would get a message indicating our phones were now working. I would think all carriers have to follow these anti-terrorism procedures. It didn't take two hours - we received a Vodaphone message within a few minutes.

Messages from Vodaphone have come in both English and Italian.

It has been great using the phones to navigate through most of Northern Italy and if we are separated which happened once on a crowded vaporetto in Venice, we could find each other although we got off at different stops.

Tanya: There are stores for all the cell phone companies at Rome Fiumicino Airport, but they're in Terminal 1 after security, so you can't use them if you're flying in from the US (arriving at Terminal 3).

So, just get it when you get to Rome. I see they all have stores in Roma Termini Station (Vodafone and Wind on the ground floor, Wind and 3 on the lower level, and TIM on the upper level). Click "Phones" on this website to see: http://www.romatermini.com/en/store/index/hi-tech