Put this in the unsubstantiated rumor category – but AppleInsider is reporting that iPhone firmware 2.2 will add support for wireless downloads:

A tipster shared with us some screenshots of the new firmware, including what appears to be the ability to download podcasts directly to your iPhone (and presumably your iPod touch). This could tidily explain why Apple rejected the Podcaster app last month. The option to “get more episodes” doesn’t appear to work in this firmware build, however.

This is different than wireless syncing; it looks you’ll be able to browse and download specific episodes. 

It’s also not clear if this will be supported just on WiFi or if it will be available on AT&T’s wireless network. If it’s supported on AT&T’s wireless network, it could ratchet up the traffic significantly.