Updating non-smartphone in family plan

Hello everyone,

we have the FamilyTalk Nation 850 with Rollover plan and I want to upgrade one phone in there.

Currently it's a Nokia 6350, just to show that there is not a fancy user behind it and it hasn't been done recently.

My problem is, that after I select the new phone we want (Nokia lumia 900), it takes me to select a voice plan, and none are the family plan. (see below)

I've tried with going with the one for $0.00, but then the data plans look like this:

Not the ones I was expecting ($20, $30 etc.). I did notice that at the top in the URL it says business (underlined). That first showed up with the overview of the phones and has been up there since.

So my questions are: How can I upgrade the phone so it stays in the family plan and we just add the $20 data plan?

Have tried firefox 14 and IE 8, cache and cookies deleted.

I'm starting to think that the AT&T website hates us.. having another problem with adding a line described here, that no one has been able to help with.