If you have an actual modem connected to the FXS of the Tenor, and you want to do modem calls, I am not sure that that will work well. Yes, the tenor states that it supports modem calls, to a small extent, but I really do not think it works well.
If you mean that the modem is a GSM or CDMA device for mobile/wireless calls, then I can help you with the config and you can contact me at mike_voip@hotmail.com