On the T-Mobile network, as well as many other cell phone networks, roaming charges can mount up quickly. If you have your phone on, and you are traveling in an area where there is no T-Mobile service (you are "roaming"), calls to your number that go to voice mail will still be charged to your account, one minute of roaming charge per message. It is often desirable to turn off the voice mail feature while traveling to avoid these roaming charges, especially if you are on vacation, but still have the ability to use your phone when you wish.
Disabling T-Mobile voice mail
Don't make the mistake of going into your phone options and changing the "call forwarding" option to avoid roaming charges. T-Mobile uses the call-forwarding feature to send your calls to a special number when you are unavailable. That number is your voice mail number. But it is set by T-Mobile's "operator-controlled provisioning" service, meaning that even though you can disable the forwarding, the next time the T-Mobile network "sees" your phone it will turn the feature back on again. If you want to be able to use your phone while traveling, the phone must have a forwarding number in it to handle unanswered calls.
T-Mobile customer service before you leave and ask them to disable voice mail for you. They do not charge for this service. Simply tell them the truth. Disabling voice mail temporarily is a common request and a simple one for the customer support representative.
You can call "611" (a free call) on your T-Mobile cell phone, or dial (800) TMOBILE from any phone to request your voice mail service be disabled.
Don't forget to call and have customer service re-enable your voice mail when you return. Unless, of course, you decide you like your phone better without it.