Hi,
I have the following Problem on my N900:
Everytime I am on 3G and want to go online the phone briefly switches to 3.5G
The pages load fine. But after a short time it falls back to 3G. Even thought the internet icon is still active, I can not access any websites. This is not a big problem because the phone switches back to 3.5G (most of the times). The problem is background tasks like pidgin. It looses the connection on 3G. And the only way to get back to 3.5G and reconnect is to open a website in the background.

So is there a way to force the phone to stay in 3.5G / UMTS?
My carrier seems not to provide internet on 3G.

No, ping some host from terminal to keep it on 3.5G as a work-around.
Its been answered before, along other, here https://talk.maemo.org/showthread.php?t=63428

oh thanks. I used google to search because usually the talk maemo threads relevant (among other useful links) pop up there but not this time.
I tried the ping workaround and its working. Surfing is way more responsive now.
ping -s 1 -q 8.8.8.8 did the trick (as posted in the thread you linked)