If the remote users have analogue modems (v34bis or V90 for example), you will need a PVDM2-DM (Digital Modem) module to terminate the speech call that comes into the BRI port.

Refer here for details -

http://www.cisco.com/en/US/products/ps6441/products_feature_guide09186a00806b941f.html

you also need a VIC2-2BRI-NT/TE voice card to accept the analogue modem calls. The BRI WIC will only work with ISDN data calls - it not work with the digital modems.