[asterisk-users] How do I tell if T.38 was used?

[Robert Moskowitz]

I am running Trixbox 2.4 which has Asterisk 1.4.18-1

I have kind of followed: 
http://www.voip-info.org/tiki-index.php?page=Asterisk%20T.38

I added to sip_general_custom.conf

;NEEDED!!!
t38pt_udptl = yes

I did not add this to the actual SIP extension, as I assumed this being 
general it applies to all sip extensions, and doing a sip show peer ext# 
did indeed come up with t38pt_udptl = yes

The fax is attached to a Grandstream 488, so I set it for fax mode: T.38

I did leave DTMF as inband (can't find any docs on what to use for this).
my rx_fax works just fine, but it did for fax pass-through.

So how do I determine if T.38 was negotiated?