When I travel to Europe/Asia, I just buy a local SIM and use Google Hangouts to make and receive calls over IP. I treat my cell phone numbers as disposable, and indeed,I've been through 4 different prepaid carriers in the past few years, but none of my friends and family noticed any change since they all call via my GV number. (well, in reality, almost no one calls these days except my parents, everyone else SMS's... I don't even answer the phone if it's not from one of my contacts since 95% of the time it's a telemarketer, and if it's not, they can leave me a message and Google will transcribe it)