VoIP XL 3600

Please Help ME!!!!!!!
I have a big problem with my cisco xl 3600 and the VoIP. If I call one internal number, in my office, from an external digital phone, for example from my mobile phone (much fast!) all works correctly but if I use an analog telephone to call the internal number in my office, I receive a busy signal, always!!!!!!

in adding the number does not come composed completely, but in part!

Help Me, NOW!NOW!NOW!NOW!NOW!NOW