Absolutely. All Signal calling and messaging is done over the internet. As long as you are connected to the internet without any restrictions, then all Signal messaging and calling will work just as it did when you were home. Your contacts can still reach you at your Signal registered number. In case you need to reinstall or re-register Signal then you need access to SMS or calls to your SIM card. Contact your mobile provider before you head abroad to make sure you can receive SMS or calls to that number if you plan on reinstalling Signal or wiping your phone while away from home.