Is it possible? Asterisk->IP to ISDN router-->ISDN to GMS GW

I have recently acquired a very well priced second hand ISDN to GSM Gateway.
I would like to integrate it to asterisk.
I am hoping that in between asterisk and GSM Gateway, I can put an isdn router (I already have one) or something else that will not be expensive and easily available.
The asterisk box is a virtual box so I’m not able to add any hardware to the machine.
Any suggestions would be appreciated.