Is there a way to make a phone number clickable on an iphone or android phone to make a call in HTML?

Something like this should work:

<a href="tel:+1-800-555-5555">Call 1-800-555-5555</a>

More info:

http://en.wikipedia.org/wiki/URI_scheme#tel:

https://www.rfc-editor.org/rfc/rfc3966