I dunno if you've got it to work yet. I had the same problem, and have the same usb modem. I managed to get mine to work without a router, and just an ethernet cable. It's quite simple, and here's how:
1- If you're on XP, navigate to your "Connect To" panel where you can see your usb modem connection, e.g "Vodafone Mobile Connect". And if you're on vista, go to network and Sharing.
2- If on XP, right-click on your internet connection and select properties. On properties, click on 'Advanced' and tick the box that says 'Allow other users to Connect through this computers internet connection'
3- You will get a little message that comes up that says that you must redial your internet connection.
4- No head over to your PS3. Make sure you've got the ethernet plugged in properly, and scroll to the 'Network settings' tab, under 'Settings'. Select "Internet Connection Settings", and click X. From here it will ask for either an easy or Custom connection. Select the easy setting, and from there it should detect your IP Address, and Clarify an internet connection from your pc to your ps3. Save these settings, and you are ready to go.
Hope this helped. If not, leave your query, and I will be glad to help more.
I fallowed all this step but after that I got the following error "IP Address timed out", but I manage to fix it and I'm going to detail what I did.
I have a Sierra Wireless card Compass 597 and I'm using Window XP ( I need to try this with Ubuntu)
1) Go to --> Start
--> Control Panel
--> Network Connections
2) Now select the mobile broadband connection (mine was called Mobile)
--> Right-Click on it
--> Properties
--> Advanced
3) At the bottom theres the "Network Set Up Wizard" --> Click it
4) Press --> Next
--> Next
--> Click in the box that says "Ignore disconnected network hardware" and press Next
--> select the first option "This computer connects directly to the Internet. The other computers
on my network connect to the internet through this computer"
5) Choose the mobile connection e.g
Mobile Sierra Wireless Compass 597 EVDO Modem #3
--> Click Next
6) Now choose the private connection.
- In order to connect the PS3 to the computer you need a 'Lan connection'
mine was " Local Area Connection (Lan)"
--> Click Next.
7) Give the Computer a description or name
--> Click Next
8) Name the Network
--> Click Next
9) File and Printer sharing (its up to you if you want to share it or not)
--> Click Next
10) Then Click Next and the change will be done.
11) Go again to step 2 and Under "Network connection sharing" check the box that saids:
"Allow other networks users to connect through this computer internet connection".
Then in the Home Network Connection bar choose the Lan connection that you created in the Wizard.
In my case "Local Area Connection"
I left my IP and DNS in auto acquire for the Lan and the Shared Mobile connection. I hope this help to the people that got the timed out error (just like myself). If this work and you able to update the PS3 try to restart the PS3 because after I updated it the error happen again but after I turned of my laptop and PS3 everything was ok again.
Sper sa iti rezolve problema si sa iti functioneze.