Problem using wvdial with MultiModem GPRS

Hi,

I'm trying to get PPP running with a serial MultiModem GPRS (it's an
external serial GPRS modem).
The host OS is Fedora Core 9 32 bit, provider is AT&T. I'm using
wvdial to initiate the connection, it looks like it makes a connection
but drops right away.

/var/log/messages shows this after a wvdial run:

Feb 5 15:43:01 linuxbox pppd[11202]: pppd 2.4.4 started by root, uid
0
Feb 5 15:43:01 linuxbox pppd[11202]: Using interface ppp0
Feb 5 15:43:01 linuxbox pppd[11202]: Connect: ppp0 <--> /dev/ttyS1
Feb 5 15:43:04 linuxbox pppd[11202]: Remote message: Welcome!
Feb 5 15:43:04 linuxbox pppd[11202]: PAP authentication succeeded
Feb 5 15:43:04 linuxbox pppd[11202]: not replacing existing default
route via 192.168.5.1
Feb 5 15:43:04 linuxbox pppd[11202]: local IP address
192.168.111.112
Feb 5 15:43:04 linuxbox pppd[11202]: remote IP address
192.168.111.111
Feb 5 15:43:04 linuxbox pppd[11202]: LCP terminated by peer
Feb 5 15:43:04 linuxbox pppd[11202]: Connect time 0.0 minutes.
Feb 5 15:43:04 linuxbox pppd[11202]: Sent 0 bytes, received 0 bytes.
Feb 5 15:43:04 linuxbox pppd[11202]: Modem hangup
Feb 5 15:43:04 linuxbox pppd[11202]: Connection terminated.
Feb 5 15:43:04 linuxbox pppd[11202]: Exit.

my /etc/wvdial.conf file is:
[Dialer Defaults]
Modem = /dev/ttyS1
Baud = 115200
Init1 = AT+CGDCONT=1,"IP","PROXY"
Init2 =
Init3 =
Area Code =
Phone = *99***1#
Ask Password = 0
Username = internet
Password = internet
Dial Command = ATDT
Stupid Mode = 1
Compuserve = 0
Force Address =
Idle Seconds = 0
DialMessage1 =
DialMessage2 =
ISDN = 0
Auto DNS = 1
Check Def Route = 1

Any suggestions about what could be wrong?
Thkx, Fred