I reckon they'll do a Vita phone down the line, but I think they couldn't get the hardware / design to work right for launch. Give it a year or two to redo the layout and get the costs down and it'll happen I think.
The main cheaper model will always just be a games console though and Sony absolutely shouldn't change that.
No idea why Sony should pull out of handheld gaming either... it's expensive but they have a lot of IP which can sell them a lot of software. You don't need to beat Nintendo to make it a success, hell the GameCube sold like 20m and Nintendo managed to do fine during that era.