Probably also very expensive
The most basic thing that you need to understand is that GPRS is a packet-based transport - that’s what the ‘P’ stands for!
I guess that the specific packet-based transport that you intend using is IP (Internet Protocol) - yes?
In that case, you will need (at least) a basic undrstanding of IP networking - this is not specific to GPRS or Sierra Wireless, so any general text will do; eg,
The biggest problem with IP in the context of GPRS is that you only get a Private IP address - unless you specifically pay for a “premium” service with a Public IP address.
This means that it is not possible to communicate directly between GPRS devices; eg, see:
There is an Application Note which describes that.