If you've setup the Phone to use drei.at try to figure out the CID from the phone.
The data accounts *should* be listed by CID number.
Let's say your data account is number #3 use this as phone number:

*99***3# (i.e. *99***<cid># where <cid> is the CID number)

on my SE phone I had to use the CID number to make it work.