Some time ago I managed to get mobile Internet with my old Huawei E220 and a turn on telkomsel SimPati Prepaid account. I had some help from the nice ladies at the Telkomsel shop here in Bengkulu. Telkomsel is much better then German Telekom, you get served and technical advise by the stuff!
One precondition is that they turn on the 3G option of your simcard, which is not on normally. You can either ask at the Telkomsel shop or do this via sms.
I use a MacBook 2 with OS 10.6.3 and a Huawei E220
Here is how it work for my mac:
1.Connect the Modem via USB to the MacBook.
2.Go to System Preferences and Network
3.Enter the following:
Telephone Number: *99#
Account name: wap
4.under Advanced / Modem
5.under PPP check the TCP Header compression box
Billing wise I use the prepaid simpati, its better to get a Which you can do from your Mobile: type *100# and then go Data Mania then choose your plan, I went for 400 MB and hope this is enough. It costs 125.000 IDR.