You can mimic the default jQuery plugin behaviour as follows: Test if the form is valid; if not prevent the default action from occurring using preventDefault(): EDIT: this comes in handy if you want to fine-tune your validation test i.e. validating some controls conditionally.
Your regex should be something like [0-9\-\(\)\s]+. It matches numbers, dashes, parentheses and space. If you need something more strict, matching just your example, try this: ([0-9]{10})|(\([0-9]{3}\)\s+[0-9]{3}\-[0-9]{4})
You could use the submitHandler option. Basically put the $.ajax call inside this handler, i.e. invert it with the validation setup logic. The jQuery.validate plugin will invoke the submit handler if the validation has passed.