Some questions about this phone

Hi all

Last week I was given a HTC Touch HD phone.

I had been using the HTC TyTnII for a year or so with no issues and was looking forward to using the Touch.

The HTC Touch HD I was given was bought from Telstra (has their logo on the back) and all the software on the phone tries to connect with bigpond.

My issue is, my phone carrier is TPG (Optus) and apart from texing and making phone calls, nothing else works... not even picture messaging.

I called TPG and they emailed me some crappy generic instructions that mean nothing.

Can anyone help me to make it connect to tpg GPRS instead of bigpond?

Any help appreciated.

Thanks