It\u2019s difficult to decide whether to laud the recent announcement by AT&T Wireless and Cingular Wireless that their respective Multimedia Messaging Services are now interoperable - or to be stunned that, so close to the wrap-up of their merger, it was not a fait accompli until now.The MMS interoperability announcement means MMS customers of each carrier can now exchange multimedia messages with users on the other carrier\u2019s network, too. These are messages that might include text, photos, animated graphics, voicemail, music and video clips.Common industry wisdom says this move is kind of a no-brainer since, soon, the two networks should theoretically be one, and it won\u2019t do for services from one entity to not work with one another.On the other hand, MMS inter-network interoperability remains rare, so hopefully the move will inspire interoperability moves elsewhere among competing carriers.As the industry learned with Short Message Service (SMS), MMS, too, will require interoperability among different carrier networks to become commonly used. Would you only want to call someone who happened to use the same phone company you did? Would you only wish to e-mail someone who used the same ISP that you did?The pokiness with which the cellular carriers in general have offered interoperability among their networks, particularly for data services, begs the question: Are they not interested in the potentially higher revenue that these value-added services might bring? Or is the issue one of bandwidth constraints and potentially cannibalizing their secure voice revenue?Voice is the moneymaker for cellular carriers. Wireless veteran and consultant Andy Seybold told a recent meeting of Silicon Valley\u2019s Wireless Communications Alliance that no data-only wireless service other than paging has ever made money.The build-outs of 2.5G and 3G networks were initially intended to add increasing numbers of voice callers to the cellular infrastructure. If we gobble up too much bandwidth using highfalutin\u2019 data and multimedia services, perhaps the carriers figure that the \u201ccan you hear me now?\u201d guy will no longer be able to get anyone to answer.