This is the calling one (probably more useful if the clickable text is words, as the iPhone auto-detects phone numbers and does this automatically):
This is the SMS one, which overrides the default calling behavior:
<a href="sms:1-408-555-1212">New SMS Message</a>
Not sure what other things these links might work on... Might be a little dangerous as having non-standard links that don't work or bring up errors is kinda bad UX. Best for mobile-only sites. If someone know if this works on Android/Blackberry/Other Mobile, comment below.