Modem Config for PBX

I have a Nortel Op. 11 C with a US Robotics modem configured for remote access. I’m having problems with it. I already changed ports, modems, speed but when I access remotely it only gives me garbage.
Can anyone help me? In the same matter, does anyone has the config for another modem, a Motorola 3460 Fast ‘R’?
Thanx.