Need Help with Changing MMS Settings

[Jahsbud]

I have a 3g with the 3.0 firmware. I was wondering on how to change the settings to enable MMS. I know I need to go to Settings>General>Network>Cellular Data Network and then put the following:
APN: wap.voicestream.com
Username:
Password:
MMSC: 216.155.174.84/servlets/mms
MMS Proxy 216.155.165.50:8080
MMS Max Message Size:
MMS UA Prof URL:,

but Im not sure how to get to the cellular data network option it doesnt show up after I go to Settings>General>Network. I installed internet tethering from help.BenM.at but I'm not sure where to go from there. Ive tried linking my iPhone and MacBook but haven't yet succeeded.

If someone could give me some step by step instruction on how to get the Cellular Data Network option I would greatly appreciate it.

Solved my own problem. It was the T-Mobile Carrier package on cydia that took away the cellular data network option