Nothing has resolved this issue as of yet. I have given up. Dell eventually offered to refund the cost of the WWAN card, which suggests this is a pretty major problem - I'd advise calling them and trying to get your money back (even return the laptop if it's a critical issue).
I have abandoned trying to use the internal WWAN modem and now rely on a USB stick from my network. Very disappointed in Dell.
Sorry I can't be of more help.