In November AT&T stated that tethering for the iPhone (the ability to use it as a modem for a computer) was coming, sometime in 2009. Of course, the best time for such an announcement would be either Macworld or WWDC. Rumors are that the tethering plans may be announced this week.
According to TUAW, while perhaps not keynote-worthy (guess we'll know after the keynote), the tethering plan may still be announced during Macworld, perhaps as a press release.
It would make sense, as would the rumored pricing and details: 5GB, $30 / month, same as with the BlackBerry tethering plan.
Of course, while the details and pricing, as well as a potential announcement makes sense, does it make sense to buy a tethering plan for your iPhone (or BlackBerry, for that matter). Personally, no. I already feel like paying $30 for "unlimited" service should allow me to tether. And don't get me started on SMS charges.
It makes me wish I had managed to pick up Netshare when it was available, however.