Now we're getting somewhere... Transferring does work between stations in the office. What doesn't work is when someone picks up a call at the front desk from their phone (brdg-appr) and then tries to transfer that call to another station in the office.. Here is the output of the trace when we try that..
10:07:19 Calling party station 3250 cid 0x2996
10:07:19 Calling Number & Name 3250 Atkins, Matt
10:07:19 dial 3788
10:07:19 ring station 3788 cid 0x2996
10:07:19 G711MU ss

ff ps:20 rn:2/1 10.93.202.5:2506 10.93.205.114:2144
10:07:19 xoip: fax

T modem

T tty:US uid:0x23b cid:0x2996
10:07:21 active station 3773 cid 0x2996
10:07:37 conf/tran hold station 3773 cid 0x2996
10:07:37 denial event 1644: Orig block/invalid digits D1=0x8be2 D2=0x299c
10:07:37 active station 3773 cid 0x299c
10:07:40 unhold station 3773 cid 0x2996
10:07:40 conf/tran hold station 3773 cid 0x2996
10:07:53 unhold station 3773 cid 0x2996
10:08:04 idle station 3250 cid 0x2996