Coexistence of iBurst and LAN connection?

[pnuts2]

Hey guys, new to ubuntu here. Can anyone please help me with the following problem?

Currently, I have two ways of connecting to the internet.

1) iburst, via USB modem.
2) college LAN.

I successfully set up the iBurst services using one of the guides on line and it is
working perfectly OK "if I disable the LAN port". Whenever I activate my LAN port all
internet traffic seem to be diverted through the LAN port instead of my activated
iBurst port.

This is somehow annoying because I have a NAS set up as well and I often need to read
files from it. I would like to do this without allowing internet to go through LAN
since it costs heaps more money than my iBurst. I am able to achieve the following in
windows without any configuration

1) normal internet service via iBurst
2) concurrent access to my NAS via LAN

Can anyone suggest how to fix this problem? Below is the output of my ifconfig

brian@Kurama:~$ ifconfig
eth0 Link encap:Ethernet HWaddr 00:15:f2:94:ec:f0
inet6 addr: fe80::215:f2ff:fe94:ecf0/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:15566 errors:0 dropped:0 overruns:0 frame:0
TX packets:34802 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1545390 (1.4 MB) TX bytes:114795232 (109.4 MB)
Interrupt:18 Base address:0xa000

ib0 Link encap:Ethernet HWaddr 00:c0:ee:0c:14:71
inet6 addr: fe80::2c0:eeff:fe0c:1471/64 Scope:Link
UP BROADCAST RUNNING NOARP PROMISC DYNAMIC MTU:1500 Metric:1
RX packets:189 errors:0 dropped:0 overruns:0 frame:0
TX packets:9369 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:149760 (146.2 KB) TX bytes:94399 (92.1 KB)

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:18 errors:0 dropped:0 overruns:0 frame:0
TX packets:18 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:900 (900.0 B) TX bytes:900 (900.0 B)

ppp0 Link encap:Point-to-Point Protocol
inet addr:125.253.44.206 P-t-P:125.253.44.1 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1456 Metric:1
RX packets:170 errors:0 dropped:0 overruns:0 frame:0
TX packets:185 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:146789 (143.3 KB) TX bytes:17829 (17.4 KB)

Thanks a lot!