According to Engadget:
This doesn't really surprise me. Yesterday a BN representative told me that they were all out of 3G Nooks, and that it could take up to two weeks for them to be able to send us out a replacement for my daughter.
So it's probably going to be WiFi only from here on out.
I really hate to think that I bought a 3G Nook for full price last year along with a two year warranty, and that I might not be able to get it replaced if I need to one year from now.