Internet problems with Samsung B3100

Hello, I hope you can help me.
My partner and I both have vanilla Samsung B3110 handsets, which were purchased brand new on 7th April 2010.
Both handsets are having the same problem.

We put our sims in the phones, and got the wap and mms settings directly from the network, which were automatically sent by text.
We then went on to Facebook, using the in-built widget and posted status updates, which suggests that the internet works.
We have also made and received calls, sent and received texts, which suggests that those settings are all OK.

The problem is with external websites and browsers, which won't run.
I downloaded operamini, which went through the download sequence, but it would not install.
It said that the internet settings were incorrect, no matter which version I downloaded.
I tried signed and unsigned versions, and various ;incarnations; such as opera 5 beta, opera 4.2 and opera 3 - all of which were unsuccessful.

I don't understand how the internet settings can be incorrect, as Facebook is working fine.
Obviously, it is slow, as the handset is 2g, not 3g.
I would still expect it to work, though.

Any ideas anyone?