Thanks for the Input ; First of all before I begin.
After all trial and error and some little bit of learning from Linux.org and other net surfing I have made the USB modem (Huawei e173 u1) work on my Raspberry Pi. (Though the Pi freezes couple of time in a week... which is another issues to be resolved).
Here are the Steps that I Followed to get the USB modem (Huawei E173 u1) going;
0) After you have the Pi up and running with all normal updates... Upgrades... etc..etc.. as per the Standard
www.RaspberryPi.org
1) Plugin the USB modem with an active SIM card in it.
2) then 'lsusb'
3) check the Modem ID... which looks like ... 'ID 12d1:1506'
4) this confirms your modem is in place and USB is detected.
5) Now type 'sudo apt-get install usb-modeswitch'
6) once done reboot the Pi.
7) Check for 'slusb' to confirm the USB modem is detected.
8) if all is going well you will get something similar to 'ID 12d1:1506 or ID 12d1:1510' (note this ID for use in step 18 as USB_MODEM= "ID 12d1: nnnn").
9) now type ' sudo apt-get install ppp '
10) then type into which ever folder you want it ' sudo wget "http://sourceforge.net/projects/vim-n4n0/files/sakis3g.tar.gz" '
11) then ' sudo gunzip sakis3g.tar.gz '
12) then ' sudo tar -xvf sakis3g.tar '
13) then make the file executable with ' sudo chmod +x sakis3g '
14) then ' sudo apt-get install libusb-dev ' this is have all USB lib
15) then ' sudo ./sakis3g recompile ' Now cross your finger and have some thrill to expect the output...
16) Once this step is done after a few minutes...
17) Edit the config file - type ' sudo nano /etc/sakis3g.conf '
18) In the file have the below lines...
OTHER="USBMODEM"
USBMODEM="ID from step 8 of lsusb"
USBINTERFACE="0"
APN="APN of service provider/SIM"
APN_USER="user name from service provider/SIM"
APN_PASS="password from service provider/SIM"
19) now from the folder in which the sakis3g is placed do ' sudo ./sakis3g connect '
And bingo here we go with the connection and the light should stay without a blink.
(incase this does not work change the - USBINTERFACE="1" , then give it a try).
Have fun. I found this working for me .... but I failed with wvdial. Any one has a better option do share.