Propably it's a shame to admit, but i've a prepaid sim card on my n900 my problem is, that tere aren't any phone numbers to change an account options during the conversation with consultant, but only express codes.
For example- when i need to buy internet transfer package i need to dial number *100*123# and push the call button.
...But it doesn't work in n900

any ideas how to make it work??

It's not implemented yet:

https://bugs.maemo.org/show_bug.cgi?id=5357