I would like to get a tradmark for a domain name.
The website that would use this domain would sell
Wireless internet access. I was wondering what
Trademark class this type of service would fall into.

Thanks in advance.

Since only one company can own a domain name at a time, it is virtually trademarked. No one else can use it as a domain name. Now if you want the domain name to also be a trademark for the company, you will have to file a regular trademark application.

More info here http://www.patents.com/trademar.htm#register-self
And here http://www.icann.org/
And here http://www.uspto.gov