My quest was to find out if there was a way I could leave my wi-fi on, but avoid any over the air charges. The rep from T-Mo got me almost all the way there. Here are the steps and advice he gave me for avoiding charges while abroad.
- Turn off data roaming. You can do this in Android by going to Settings > Wireless & Networks > Mobile Networks and unchecking Data Enabled and Data Roaming. This way your phone won't try to get its data from the T-Mo network.
- Use wi-fi calling with a caveat. I can call phones in the US for no charge using wi-fi. However, if you try to call a phone in a non-US country, even if it is in the room next you, it will be charged to your account as an international call. Wi-fi calls originate from the US, making US calls domestic and calls to anywhere else, still international.
- Don't let people call you. If you are abroad and someone calls you, even if you don't pick up and it goes to voice mail, the network had to find your phone and you'll be charged for a minute of international air time. You can stop this by setting up unconditional call forwarding, which means anyone who calls your number will go straight to voice mail without the network trying to find your phone. You can do this on any T-Mobile phone by dialing in a special code. Dialing **21*18056377249# will turn it on. Dialing ##21# will turn it off. Wunderbar!
Now, the one thing I haven't figured out how to avoid is a charge when your phone checks in with a tower. If keep my phone in airplane mode, I should be able to avoid this, but if I want to use wi-fi, I'll have to grit my teeth and take the charge. I might be able to get away if I remove the SIM card, but that's a pain to do and I don't want to carry my SIM card separately for fear of losing or damaging it.
Anyway, I thought I'd share the intel.