Brett N writes:
I'm assuming you are using a Sonus gateway? This is a known problem with Sonus. They put a few of the options (namely NPDI and RN) to the left of the "@".
are you sure that npdi and rn are not tel uri params that must be on left side of @? for example, 19.1.6 of rfc3261:
Thus, tel:+358-555-1234567;postd=pp22 becomes sip:+358-555-1234567;postd=pp22@foo.com;user=phone
-- juha