i done exactly in this order but got no results:

1) Pair up the devices (bnep0 will be created) = ifconfig doesn't show bnep0 !?
2) Start the Internet connection on N900 (gprs0 will be created) = ok
3) Start the script on N900 (the forwarding, routing and DHCP established) = ok
4) Press "Acces Internet" = on the previous screenshot it' number 5

so i tried to tether from ubuntu 10.04 (lts) (blueman + NMPANSupport plugin) to asus eeepad and it works (screenshot below)

and i tried to tether from n900 (with your script) to ubuntu and it also works !!

It gets frustrating not to understand what is happening.
The only thing that may seem problematic to me, is the point of creating a bnep0 when pairing.
bnep0 only appears when I press on the "Use internet access eeepad" screenshot 5 in the previous post.

ubuntu sharing its connection on asus eee pad transformer = lagging but works



9000: it's the last screenshot on my previous post. And it's says no network.