Updating the DNIS using the GUI on a TA908e causes the SIP trunk to fail.
If your SIP trunk is set to use UDP and then you add a DNIS Substitution, both the trunk SIP Server and SIP Registrar are reset to TCP thereby causing your once working trunk to fail.
AOS Version R11.2.0.E
Boot ROM Version 14.05.00.SA
Hope this helps someone.