Hi,
I have an n900 an 3G isn't working on any network with UMTS 900
Optus, and Vodaphone are both 3G networks with UMTS 900, but when I try connecting to them they say 'no access' I can only get 2g with their networks.

Also note that both networks have UMTS2100, and that isn't working either.

It would just be a 3G problem, but Telstra, which is a UMTS 850/UMTS 2100 network works fine .
So I'm guessing the issue is with UMTS 900 supported networks?? Any ideas how to fix my phone?
My friends have the same phone and it works fine on those networks.
I reflashed with the nokia firmware update tool, still only getting 2G on optus and vodaphone..

Hope someone can help..

Just to be certain, is your SIM card 3G-enabled from your carrier? I.e. does it work on 3G in another phone, for example?

Did you make sure your carrier allows the N900 to get on the network at 3G? I remember seeing a chart somewhere stating which networks allow 3G and which lock you too 2G [AT&T for example in the US locks the phone to 2G, no matter what]. Call your service provider and find out if this is the case first, if it is, switching cards and doing mods wont help at all.

pretty sure it isn't that, spent a whole day and bought simcards for every network in Australia and replaced my simcard. I have friends on optus and virgin with n900s (same network as mine) and they work fine. I even got a second optus simcard, and I got my simcard replaced, same issue.

My phone is stuck on 2g, with both optus and Vodaphone, which are both UMTS 900/2100 It only gets 3G with telstra, which is UMTS 850/2100...

which firmware image did you use when you flashed your device?

if you took the US image it could be that the UMTS modi you need are deactivated. try flashing again with the global image.

also, please post the exact firmware version of your friends N900 where it works, and the one you use.