I think 3.5G will consume much more battery than on 3G? On the Nokia E90 it was so. It think for battery live it would be good to fix it ti 3G

So ..like.. there is no way to make it stay at 3.5 during data and at just 3g during everything else. Like there is a way to let it stay at just 3g/3.5 or 2g/3.5/3g or just 2g. There is like an app for that... Like hope it helps.

3g/3.5g mode is controlled by the network.

Wrong - on my Nokia E90 I can enable or disable it. I have then 3G or 3.5G. Please dont confuse the people with such statements - thank you.

So on your E90 you can disable 3.5g, while keeping 3g enabled, is that what you're saying?

I imagine that can be done.. However, if the phone tells the network that it supports 3.5g/hsdpa, then the network fully controls when 3g or 3.5g is used...

It will switch to 3.5G on demand (when possible) for transferring big chunks of data then back to 3G when there's little/no traffic (or when the signal drops too low). I see it all the time when I'm using mine (when I have a decent signal). If I download a tiny webpage that pulls in extremely quickly, it doesn't switch. If I download something that takes more than a second (maybe a fraction of a second), it switches to 3.5. When done... after a few seconds it switches back to 3G to conserve battery.

Why would you want to suck the battery dry when you don't need to (when you're not transferring data)? The battery in these things is already horribly inadequate.
That would be like locking the CPU at the max clock rate all the time instead of allowing it to throttle.

(That reminds me - I have to contact the manufacturers of some of my external battery packs to have them send me a microusb connector so I can charge this thing on the go)

Correct. It saves much battery on my E90.