FollowMe/Disa difference, IAX trunk

Hi;

When I call my trixbox with my cellphone, get a DISA, and call out using the same trunk, my trixbox gets eliminated from the connection after 25 seconds, which is very good for audio quality. (My motivation for doing this, is to keep people from calling my cellphone number, I want to stay with one number, and never reveal my cellphone caller id.)

For the opposite connection, somebody calls my trixbox, and the FollowMe feature dials out to the cellphone, the connection goes through my trixbox for the whole duration of the call, and audio quality is sometimes bad, probably limited by my upload speed.

Can anybody shed some light on why the origination/termination bypasses my trixbox in one case, but not the other.

Jan