Sam is a Google Voice user, which is good news because this will mean his Google Voice number will forward his calls to any phone. He's more worried about the services he uses on Android not working in China. For this, he can check this Wikipedia page to see what sites and services are working in China at any given moment. Leo can't be certain that Google Voice will continue to work in China, although has used Skype with great results there. Leo thinks that he's more likely to have an iPhone work than Android, but he thinks both are pretty widespread and used.
The chatroom posted a link from PCMag about leaving your mobile devices at home for security reasons in China, but Leo wouldn't go that far.