Two issues:
1. The phone number area code field allows only TWO digits. The third digit falls behind the parentheses.
2. After adding the code to the form I tested it. The phone number was no where to be found in the received email.
the form:
<p>Your Name (required)
[text* your-name] </p>
<p>Your Email (required)
[email* your-email] </p>
<p>Your Phone
[phone your phone number] </p>
<p>Subject
[text your-subject] </p>
<p>Your Message
[textarea your-message] </p>
<p>[submit "Send"]</p>
http://wordpress.org/extend/plugins/contact-form-7-phone-mask-module/