lestag: As i understand it the internal GPS is a feature not enabled on the telecom network, more to do with 111 situations than a full GPS device. I have never been able to get a satellite fix with just using the internal GPS. I take it you have??
I am no expert but I think what you are talking about is AGPS (Assisted GPS) which uses cell towers when there is no GPS coverage available due to being indoors or cell phone in pocket etc. This is not available (to my knowledge) on Telecom. In theory it is possible to provide crude positioning using cell towers alone - accuracy dependent on the number of cell towers (and their position) within range.
However, GPS is completely independent of Telecom. The internal GPS is a hardware device that was enabled by the recent ROM upgrade. I have managed to get the GPS working but it takes a long time to get an initial position fix (5-10 minutes) and you need to have a clear view of a lot of sky. Once it has established its position, it seems to be fairly tolerant though - I can drive around with the phone in the car without it losing its position.