http://www.inavx.net/

or in iTunes:

AppStore > Navigation > iNavX Marine Navigation and Charting

I have a 1st generation iPhone and it is finding where I'm at via the celphone tower and my wifi connex.

It's kewl. I'm downloading the charts, which are already listed, right from the phone. Ergo not having to go download the bsb's via Safari - it's all right in there.

Joe Bob says go check it out.