Does anybody know the specifics on a SimPlus network?
Yep - you want to pay for a specific data package.
Dial *110#, select option 5, then you have a list of data packages to choose from. Simplus is quite pricey for data though - 35zl for 0.5GB. And whatever you do, make sure that you always have a data package - I think it's about 2gr for 10kb of transfer if you don't.
You can check how much data you have left by dialling *121#