Yahoo and Sprint have hooked up with  software company Seven Networks, a leader in wireless mobile data transfer, to provide inexpensive access to mobile email.  Wednesday, the three companies started selling access to Yahoo Mail for Mobile for $2.99 a month (U.S.) plus air time as compared to $40 month for BlackBerry Service.  Initialy, the service will run on select units made by Sanyo, Samsung, and PalmOne and is available only in the United States.