the TEL: tag is usable by mobile phone web browsers, as used in Menu Choice 2. (try it on your mobile phone's web browser)
the CALLTO: tag is usable by Skype enhanced web browsers, as used in Menu Choice 3 (try it on a Skype enhanced web browser on your PC or Mac). CALLTO: is also used in Micosoft's NetMeeting and Outlook. (Isn't that interesting!)
Skype enhances web browsers by letting users download an "add-on" or "plug-in" with code that gets attached to a PC or Mac's web browser. The Phone Manufacturers use TEL:, and since PHone PHriendly is trying to be usable by mobile phones, that is the tag we're using here.
Convince us otherwise.
I should like to note that the Blazer browser on my Treo 650 picks up the telephone number that is in the text, and hyperlinks it to the phones software. I'm offerred a choice to dial the number as a voice call, send a text message, or cancel. They probably pick up on the "+" character followed by the digits of a Country Code as defined in ITU Reccommendation E.164 - and continues to pick up any digits that follow until an alpha-character comes along. Skype also finds the number in the text, but has trouble dialing it on the Macintosh platform.
TEL URI - Telephone Number Uniform Reference Indictors