If your cousin's cellphone is on Sprint PCS and yours is on Voicestream, in the past you couldn't send text messages. But with Intercarrier messaging, rolling out now, you can send text directly to any cell number. The service is limited to text for now. Enhanced Messaging Service, which supports graphics, and Multimedia Messaging Service (pictures, audio, and video) are still available only to intra-carrier subscribers.
—Suzanne Kantra Kirschner