PPP hangs-up before completing T-Mobile connection

[Jim0000001]

I'm trying to dial out on a GSM modem to a T-Mobile APN
(epc.tmobile.com). However, pppd hangs-up before obtaining an IP
address. Can anyone tell me why I'm not getting a connection with an
IP address?
The ppp session looks like this:
-------------------------------
-bash-4.0# pppd call tmobileGsm
Starting Sierra Wireless GSM connect script...
Setting the abort string
Initializing modem
Setting APN
Dialing...
Serial connection established.
using channel 41
Using interface ppp0
Connect: ppp0 <--> /dev/ttySierraAT
sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x31a77a57> <pcomp>
<accomp>] rcvd [LCP ConfReq id=0x27 <asyncmap 0x0> <auth chap MD5>
<magic
0x730ab6a3> <pcomp> <accomp>]
sent [LCP ConfAck id=0x27 <asyncmap 0x0> <auth chap MD5> <magic
0x730ab6a3> <pcomp> <accomp>]
rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0x31a77a57> <pcomp>
<accomp>] rcvd [LCP DiscReq id=0x28 magic=0x730ab6a3] rcvd [CHAP
Challenge id=0x1 <4e8ec9fb06249e6d223e4fa904817891>, name =
"UMTS_CHAP_SRVR"] sent [CHAP Response id=0x1
<54a5a4872d90fa1b7e2c85b8ce9debc7>, name = "scu1"] rcvd [CHAP Success
id=0x1 ""] CHAP authentication succeeded CHAP authentication succeeded
sent [IPCP ConfReq id=0x1 <compress VJ 0f 01> <addr 0.0.0.0> <ms-dns1
0.0.0.0> <ms-dns3 0.0.0.0>] Modem hangup Connection terminated.
-bash-4.0#
========================
Here is tmobileGsm:
---------------------------------------
-detach
/dev/ttySierraAT
460800
debug
defaultroute
usepeerdns
noccp
crtscts
lock
connect '/usr/sbin/chat -v -t6 -f /etc/ppp/peers/
tmobileGsm.connect.chat'
========================
Here is the options file:
---------------------------------------
lock
noipdefault
========================
Here is the chap-secrets file:
-----------------
# client server secret IP addresses
* * *
========================

Any help is very much appreciated.
Jim