I can recieve them but for some reason I can't send them. What do I need to change (settings) or what am I doing wrong?

BTW, I'm using a E61

Make sure that your message center settings are correct.

Menu > Messag. > Options > Settings > Text Message > Message centre in use

-riannn

I'm having the same issue with not being able to send text messages with T-Mobile USA. I can receive them though fine.

In Messaging | Settings | Text Message | Message centres | ...

Msg. centre name : Message centre
Msg. centre number: +12063130004

I confirmed the message centre number with the T-Mobile site.

I have the other settings as follows:

Message centres
Msg. centre in use: Message centre
Character encoding: Full support
Receive report: No
Message validity: 24 hours
Message sent as: Text
Preferred conn.: GSM/UMTS (tried Packet Data too that didn't work)
Receive report: No

Any thoughts? I love this E61. I've got everything working except text messaging (including Bluetooth wireless modem!!).

Did anybody find the solution for this?