So, two days I bought a "one-week old" 5800 XM NAM off a guy. Last night I suddenly noticed that my new phone wasn't receiving any text messages, though it was sending them.
I began searching various forums and discovered that there seems to be a bit of an epidemic of this failure in Nokia phones, with no clear consensus on what to do to resolve the problem. In some cases, it seemed that the only solution was to change phones. But, here's what I did.
First, I backed up my phone using the Backup feature. Then I did a hard reset by dialing *#7370#. After this I was still unable to receive any text messages.
Next, I called Fido and asked them to disable and then re-enable my SMS service. The rep said that he had heard that helped in some cases. But nope, not in mine.
Third, I reinstalled the latest software update** 20.0.214 (guessing), and still no change.
Fourth, I got in my car (sorry, I would have used my bicycle but I'm ill today) and drove to a Fido kiosk. I asked the rep to help me investigate the possibility that my SIM card was defective. She put my SIM card in another phone, and it still couldn't receive any text messages. Next, she put her SIM card in my phone and it could receive text messages. Great, at least we know that the phone is not defective! She asked a customer service at the call centre to "totally reset my account" (her words), after which I was once again able to receive text messages.
If you're having problems, try these steps, and good luck.
** [Note, reinstalling the latest software update required me to dig out my old Windows PC, since Nokia PC Suite refused to install in Windows XP running in Parallels on my Mac. And my old PC didn't initially have enough room left on the drive for the install so I had to spend an hour deleting apps and data].