What happens to iMessage if I swap out my SIM card?

Question

My wife and I are traveling to Europe this fall and plan to bring our iPhone 5c's with us. Our plan is to use local (O2, Czech Republic) SIM cards for phone and internet service, swapping in the O2 SIM when we arrive and replacing the VZW SIM when we return to the US. (We may also sign up for a VZW international plan at the same time, just in case we have problems with the O2 service.)
VZW tech support has assured me (though I will re-check before the trip) that our phones are already unlocked and will accept activation of another SIM card. Of course our phone numbers will change, but I expect our internet services, via O2 data plan or (mostly) Wi-fi, to go on like nothing happened. I understand SMS text messages will queue up in our absence. However iMessage operates over the internet, not SMS service. What happens to iMessages destined for our VZW number while the O2 SIM is in the phone? What about iMessages sent to the new number on the O2 SIM? And what happens when we return the VZW SIM to the phone? I can imagine confusion on Apple's end with the multiple services. Thanks for any guidance!

Answer 1

I'm going to call the question answered. I hadn't changed my iMessage setup since getting the phone at the Verizon store. I had to go through the process of registering my Apple ID with iMessage; dunno why that wasn't already done. But once that is done, iMessage should follow the phone just as wushu2004 and rcschnoor said. Putting the VZW SIM back in the phone returns it to its previous status -- though it may take several minutes for iMessage to change the phone number to the current SIM, don't ask me why.
I have to say I still have a difficult time understanding exactly what is going on with iMessage, though I think I finally understand that when iMessage says it's using [email protected], it's referring to my Apple ID (which is the same as my email address) and not my actual email service.
Thanks, all, for your help!