Mitelmatt,
I have connected a Quescom 200 to the 3300. Those work very very very well But....
Those are very expensive, if I'm not wrong we payed around 1100 Euros (Distributor Price)... They are SIP ready and accept 2 SIMs. The company is very well organized, contact Karine MacMillan, she speaks english and based somewhere in France.
I've also heard that 2N have a nice sollution as well, for about 700Euros. But I haven't tested these yet. This is a Chzeck Republic company
If you try the ones from 2N tell us how they go
Regards,
Daniel