If I remove my SIM card from my iPhone, will iMessage still be connected to my phone number, or can I only be reached by my Apple ID email?
I don't have an iPhone myself, but because the account can be based on email address as well, I believe it in theory should be possible to keep using iMessage after removing your sim. However, I have experienced that my friends who have gone overseas and used a different sim have ended up having iMessage being connected to the new number. In other words, it is possible to connect to you via iMessage, but your new, overseas number will need to be made known.