Bell Mobility has added access to the Twitter online social network to their service, allowing their customers to send and receive full SMS messages through their profiles. Those who sign up can use their mobiles to send and receive "tweets", the small messages that are limited to just 140 characters across the Twitter network. The catch? It will cost you 15 cents for each message sent and received. Bell is the first wireless network in Canada to offer Twitter as a built-in service.