Mobile phone number verification, ie. prove that you're a human in countryX by entering your mobile phone nr. in the US and we send you an SMS code or something. Google does (did?) that if I remember correctly.
http://blog.twilio.com/2010/05/sms-phone-verification-with-t...
http://blog.twilio.com/2010/05/simple-phone-verification-wit...
I would make a couple of points though, we've run into several sites that don't provide a mechanism to have the call retried (answering machine, undelivered cell call, etc) or to go back and enter a verification code if it was captured by voice mail etc. Google lets you enter the code whenever you get it, Twilio lets you initiate a new call with a new number, but many ignore this problem.
If you need real verification of a human and their identity, don't use phones for it. Especially not an automated phone system.
1) Provide an additional time-consuming, potentially slightly costly and hard-to-automate barrier to negate spammers (like Gmail does during signup).
2) Verify that someone controls a number before using it as an interface to your app either through notifications or control (adding appointments or tasks, etc).
Like you mention there's no way to use this method to verify someone is who they claim to be. But there aren't really any methods for this type of thing that can't be spoofed.