That's a great idea for tracking them down.  It would work for a lot of Bitcoin scammers who wouldn't think that reading an email would give away their IP address.

71.57.149.160 is c-71-57-149-160.hsd1.fl.comcast.net, a completely normal residential address.  VPN's don't use addresses like those and I've never seen a TOR exit node use one either.  Unless they're proxying through botnet controlled machines or open proxies (both unlikely IMO), it's highly likely that it's their actual home account.  Especially with the iPhone since configuring that to use anonymous proxies would be a pain.  What is the IP address from the iPhone request?

I'll do a bit more investigating of that IP, but generally the only way to get the owner's information is to subpoena the ISP which requires a court order.

Edit: It's not listed in any lists of known proxies and it's not on any blacklists.  This means it's even more likely to be the person's normal home connection.  All ports are filtered, so there's no additional information that can be gained that way (well, not currently, ports could open later though).