Well, someone's bound to come in here any minute now and grumble about how this topic has been discussed to death, but there do seem to be some interesting new signs. Besides the fact that lots of analysts are calling it, Walt Mossber of the Wall Street Journal seems to think an Apple phone is coming, and he does seem to have a good relationship with the company; he's reviewed some products too soon to have not been given advance notice. Also, that denial Def Jef mentioned, from Japanese mobile carrier SoftBank wasn't really a denial of the content of a rumor. It seemed more like damage control. The SoftBank exec didn't say "That's not true!", but something more like "We never said that!"
Also interesting is Steve's recent "no comment" about an Apple phone when he was interviewed on CNBC. I'm pretty sure he's been more assertive in the past, saying that Apple isn't doing it. When he switches to "no comment", it seems more likely.
The fact is, phones are going to provide the most competition for the iPod line, especially the lower-capacity models, in the next few years. If someone can get reasonable music-playing functionality out of a phone, which they'll always bring with them anyway, they may just forego a separate music player. If Apple managed to make the phone with the best music management available, they stand to make a lot more money by selling the hardware than by licensing the software to another phone vendor and hoping to make a few more iTMS sales.
Of course I really want this to happen, since Palm OS seems pretty much dead in the water and I want an extensible, desktop-sync-able phone with the kind of beautiful UI that Apple's good at.