I was curious too; from wikipedia:

"In contrast to other top-level domains .tel information is stored directly within the Domain Name System (DNS), within the actual domain name record, as opposed to the DNS simply returning details (such as IP addresses) of the machines on which information can be found."

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

Because .tel was approved specifically (and solely) for this purpose :) Here's Telnic's quick 5 minute pitch: http://www.youtube.com/watch?v=JnRwniqqiCE