GSM Modem "data enabled"

[sklux]

gsm data enabled calls

I know that when you are using a GSM modem to dial out a PC, you
dont need something special concerning the SIM card.
When you want to get an incoming connection on the PC you have to
use a SIM card with data enabled function.

What s the technical reason for it??

 

[throwaway18]

I once had to call my service provider to get outgoing data calls enabled. I think they mostly enable it by default now so people can use WAP. I was given two extra numbers so I had my voice number and different telephone numbers for incoming data and fax calls.