Do you have a butt set? If so tap into the line and see if you hear digits when the phones rings or after answer. I'm betting there's digits after answer. If so you'll have to get your supplier to kill the digits if you don't want them, or your modem to ignore them. Did you request the digits because after the modem answers you need the call to go to a specific message or port on your voice response system? Sounds like the T-1 and trunks are working, so from there it's how you want them to interface.
Just wanted to add, if telco isn't giving you the digits and you don't have them at the phone, they must be coming from your modems.
