When will iPhone support PPPoE internet connections?

No one here would know, suggest such to Apple:

http://www.apple.com/feedback/iphone.html

PPPoE is irrelevant to the iPhone; it is a protocol between the ISP and the first point of presence on premises, which today is almost always a wired or wireless router. PPPoE would only be meaningful if there was a way to connect the phone directly to the incoming Internet connection. As there is no way to do this physically it would be pointless.

FYI:

Providers do exist that run PPPoE on top of their wireless network.

Thanks; I admit I've never encountered it.

Overseas...sometimes in bases...it's the only connection available to these guys.