asterisk users - Jul 2015 - Asterisk and Vitelity's vMobile service

I'm trying to configure my Asterisk machine to work with Vitelity's
vMobile service.  I can place calls to the vMobile device and it rings
as expected.  However, I have no audio in either direction.  There's
no NAT involved though.  My asterisk machine has a public IP address
with port 5060 and the full range of RTP ports open.  (It does have a
second NIC and some SIP clients on the private side but I'm not using
those for my testing.)

Here's the relevant parts of my SIP.  Anyone see any obvious problems?
 Not much documentation around on vMobile.  I'd love to see a working
config if someone has one.  Thanks!

[general]
nat=no
externaddr=my_public_ip
localnet=192.168.1.0/255.255.255.0
register => username:secret at inbound23.vitelity.net:5060
bindaddr = 0.0.0.0
srvlookup=yes
alwaysauthreject=yes
transport=udp
directmedia=no
allowguest=no

; Vitelity vmobile SIP user
[my_did_here]
type=friend
dtmfmode=rfc2833
host=my_did_here.mobilet100.sipclient.org
context=vmobile-out
defaultuser=my_did_here
fromuser=my_did_here
trustrpid=yes
sendrpid=no
secret=super_secret_password
disallow=all
allow=ulaw,g726,gsm


-- 
Chris