href=tel:555 link not working in mobile safari
Your mark-up is fine, and it works on my iPhone (3GS, running 4.3.5). It doesn't work on the iOS simulator (yep, there's the "Cannot Open Page - Safari cannot open the page because the address is invalid" error), but then I wouldn't expect it to, given that you can't make calls on it (either that or the older version of iOS is at fault).
In your <head> put:
<meta name="format-detection" content="telephone=yes">
From Safari HTML Reference:
This Enables or disables automatic detection of possible phone numbers in a webpage in Safari on iOS. Syntax Discussion By default, Safari on iOS detects any string formatted like a phone number and makes it a link that calls the number. Specifying telephone=no disables this feature. Availability Available in iOS 1.0 and later. Support Level Apple extension.
for a telephone number to work in Safari/iOS you need to format the telephone properly like it would be listed in an old ad.
<a href="tel:1-555-123-4567" class="call">
----- OR -----
<a href="tel:15551234567" class="call">