Samsung Galaxy S :: Understanding GPRS Settings (New Access Point)

I recently got a new SIM card (same provider, Telkomsel, but for a different area code in Indonesia). The settings are supposed to be automatic, and I do indeed have a "Telkomsel GPRS" under "Mobile networks" > "Access Point Names". The 3G on the old SIM worked pretty well, without having to do anything, but this one gets only rare and short-lived connections to the net. I've rung up Telkomsel a few times now, and they're supposed to be fixing it soon, but it's a few days and I'm getting impatient. One of the help line people suggested manually entering a new access point, but the info he gave me was a bit confusing.