Extending the time before going to Voicemail
Posted: Fri Dec 03, 2010 11:23 am
TMobile
Sometimes you may wish to extend the delay period before someone phoning your mobile gets diverted to voice-mail. This may be because you don't get to the phone in time, or you have a ring tone that you want to listen to. 
Although this is usually deemed a network operator job that you can't control from the phone, you can actually send the relevant GSM command message from your handset.
The delay can be set from 0 to 30 seconds in 5 second increments. We'll call this 'nn'.
Key into your phone **61*destination*11*nn# [send] where 'destination' is your voice-mail number. On T-Mobile this is usually +44073 followed by your mobile number excluding the initial 0. So, for example, if your mobile number is 07946123456 you would key in **61*++440737946123456*11*25# and press [send]. This should set the voice-mail delay to 25 seconds.
To cancel, send ##61*11# and to query, send *#61*11#
Click Here for More GSM Commands