I have worked with a GSM gateway quite long before which act as a backup for a voice gateway. If i remember correctly, the GSM gateway out was rj11 which i terminated on a router with FXO cards. And created SIP trunk between this gateway and the CUCM.
As SWG-3016 data sheet shows SIP as feature and use case shows SIP trunk between Openvox PBX, So you should be able to create a sip trunk directly from SWG-3016 to CUCM.
For how to configure SIP trunk on Openvox is out of scope of this community. This you need to check with openvox.