SIM card and keeping Verizon phone number

Can not be done. If you buy a SIM card in Spain it will have a Spanish telephone number.

No, you can't keep it unless you have a dual SIM phone. If you have a phone with only one SIM slot, then you will have to remove the Verizon SIM and insert the Spanish SIM. While you have the Spanish SIM in place, you'll have a Spanish phone number.

You could set up Google Voice before leaving the states. This will give you a new, additional US phone number (free). You can use Google Hangouts to make calls to US numbers for free while in Europe, and people can call you on the Google Voice number (set Hangouts to ring for incoming calls; you'll answer calls in Hangouts). At least, you can tell people to call you on that number and text you on it. (Use the Google Voice app for texting with your Google Voice number.)

When you install Google Voice, don't have it use your Google Voice number for outgoing calls.

If you get that to work, then you can figure out how to forward your Verizon calls to the Google number while you are traveling. At least you can receive calls from people who call you.

You still won't be able to make calls out with your Verizon number. And I don't think you'll be able to send/receive texts with it.

You can also look into whether your phone supports WiFi calling. That would let you use your Verizon number for free US calls and texts while on WiFi only.

Do you know about the Verizon option to add international to your phone at $10/24 hour period? It only goes into effect if you use your data. I did this for my last trip. For navigation I used Maps.me and downloaded appropriate maps when I had wifi. Then you can use it offline like GPS. We used wifi at our hotel and then a few times when a restaurant or venue had wifi. We ended up never using the Verizon program. What would happen is that if you use your phone, you get the following 24 hours to use it for your $10. This way you'd be able to keep your phone number. Also, you will be able to receive your texts when you have wifi.

We added Verizon International plan to my spouse’s phone and I got a SIM card for my phone. We had the best situation.

Rather than the $10/day plan, there’s a 100mb plan for $25. While I still had Verizon, I’d use this and lots of WiFi- keep your phone on airplane mode! As we travel frequently outside the US, I finally switched to T-Mobile that includes international travel as part of the plan.

How many days do you get for the 100mb plan? Or is it infinite and when the data is gone that's the end?

Looks like Verizon has changed their monthly international roaming plans around. Probably good - 100mb is not going to last anyone very long (would last me a day while traveling). The new monthly plans are not great deals either, though, in my opinion. $70 for 100 min, 100 sent texts (unlimited received), 500MB of data (which would last me 5-6 days). $25 per extra 500MB of data overage. The $130 plan includes 2GB of data - makes more sense if you are going to be gone close to 3-4 weeks and can live with 2GB of data (probably doable for most people), otherwise, for a trip of 13 days or less, you would be better off with the $10/day unlimited plan.

https://www.verizonwireless.com/solutions-and-services/international-travel/