Okay, and just to make matters weirder, I could log into my WordPress install (same account/password but for some reason you have to login again when you go over to bbpress) on the same iPhone.
AND I could log into the bbpress side on a different iPhone (borrowed one from somebody). But on my own iPhone I suddenly can’t. And I’ve been doing it successfully for years.
Did you try installing a new keyboard on the phone? Are you current with all system updates?