How do I force my 8900 to used edge insytead of gprs?

Wirelessly posted (8320 Titanium)

as far as I know, you can't. Certain towers have different capabilities...towers near my house (in a smaller town) are GPRS...going to the neighboring bigger cities, I get EDGE...I think its just how it goes. If I were able to tell my phone not to use GPRS, I wouldn't have service at my house since there isn't an EDGE signal close enough.

You won't be able to use EDGE unless your carrier provides that service. Also, does your screen say "gprs" or "GPRS"? If it says "gprs", then you need to purchase a BlackBerry data plan.

Assuming you are on Orange UK, you can use this to see what coverage is available
Orange UK mobile coverage