Networking Issues

I have wlan0 and ppp0 connections. I can reach the internet with my wlan0 connection, but not with my ppp0 connection.
My ppp0 is an external serial 56k modem. I am running Ubuntu and have tried using the Networking gui, pppconfig, and gnome-ppp but all of them give me the same result. A connection is established, but Linux can't seem to realize that it is available for use.

Here is my routing table when both are on:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.5.96.65      0.0.0.0         255.255.255.255 UH        0 0          0 ppp0
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 wlan0
0.0.0.0         192.168.2.1     0.0.0.0         UG        0 0          0 wlan0

Here is my routing table when just ppp0 is on:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.5.96.65      0.0.0.0         255.255.255.255 UH        0 0          0 ppp0

Here is my routing table with just wlan0 on:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
192.168.2.0     0.0.0.0         255.255.255.0   U         0 0          0 wlan0
0.0.0.0         192.168.2.1     0.0.0.0         UG        0 0          0 wlan0

I noticed that the main differences lie in the flags "U" vs "UH" and the lack of a "UG" entry for my ppp0. Is this of note?

I've tried using route add with my ppp0, but that doesn't seem to help. Is there a way to set up my ppp0 such that it will be used as a gateway when wlan0 is not connected?

Where else should I look?