I really need to note this in a few sentences.

If you ever encounter the problem, that you cannot establish a VPN/PPTP connection using A1 UMTS; Call them, tell them they are stupid and should deactivate the firewall.

Oh yes. You read correctly. They now have a firewall, that actually blocks the GRE protocol (outgoing).

Is this stupid? Yes. Very stupid!

Perfect service A1! Makes more problems than it helps!