problem with multi-site user

[blackburnrovers]

There are two sites which i will call A and B. they have a T1 connecting them. Voicemail is only at site A. When a user calls an ext. from A to B it rings just fine. but if they don't pick up it should go to their voicemail. it doesn't. what happens is that it will ring at the phone at site B for the amount of rings before it goes to voicemail and then the icon will flash on the target line and sit there. user at A just hears ring no answer.?????
they can call voicemail from site B just fine. all routes and dest. codes are fine. what is going on?
please respond.