I have a t-mobile sim card, but my phone is htc

You need the T-Mobile settings if you are using a T-Mobile SIM. assuming you are in US as Unicel not over her in UK so the settings are:

T-Mobile GPRS settings (T-Mobile EDGE settings) T-Mobile GPRS/EDGE settings for terminals (e.g., phone handsets). Some items are possibly Nokia-specific. I have found the authentication type can be either Secure or Normal. These settings should be useful for T-MobileWeb users.
APN: wap.voicestream.com IP address: 216.155.165.050 Data bearer: GPRS Username: [none] Password: [none] Authentication type: Secure Connection security: Off
APN is the GPRS Access Point Name.
T-Mobile GPRS/EDGE modem settings T-Mobile GPRS/EDGE network settings when using a device as a GPRS "modem", that is, when "tethered" to another device. Examples include connection via Dial Up Networking (DUN) Bluetooth profile, or via Universal Serial Bus (USB). These settings should be useful for T-Mobile Internet users.
APN: internet2.voicestream.com Username: voicestream Password: [none] SMTP server: myemail.t-mobile.com
APN is the GPRS Access Point Name.