Each phone does it a little differently! Are you trying to forward calls from your cell phone somewhere else, or calls from somewhere else to your T-Mobile phone?
I am trying to forward calls and texts from my T-mobile S6 to my work phone (also an S6).
T-Mobile does not offer a service which forwards text messages. You may be able to do so with a 3rd party app.
What it does
Turn on unconditional forwarding (CFU) to a number.
Turn off unconditional forwarding.
Turn on forwarding if no reply (CF NRY) to a number.
Turn off forwarding if no reply.
Turn on when not reachable (CF NRC).
Turn off call forwarding when not reachable.
Turn on call forwarding when busy (CFB).
Turn off call forwarding when busy.
(For example, 5 seconds, 10, 15, etc.)
Change the call forwarding delay time (5-30 seconds).
Turn on call waiting.
Turn off call waiting.
Blocks outgoing Caller ID on a per-call basis. This does NOT prevent the display of your information when you dial certain business numbers, including 911, 900 numbers, or toll-free numbers.
Cancel all call forwarding.
Really great info... if I have pay-as-you-go, does my plan still get charged for the call even though it has been forwarded to a new number?
Yes. Any call associated with your telephone number will be charged to your line.
Cool... thanks for your timely reply!
How do forward my calls and text messages without access to my phone as it is damaged and awaiting warranty exchange replacement?
The codes I read must be dialed by the phone with your number. To initiate CF the command must be initialized by the forwarding number. Messages cannot be forwarded. If you have or had an iPhone iPod or Mac you might be able to see iMessages.