There is such a thing. They work great but I can't for the life of me find them online. They basically have small rubber buttons at the end of each finger which works with the iphone so you don't have to take your gloves off. Alternatively there was one with a trackpad on the wrist that you could use somehow connected to the iphone.
Come to think of it, I believe they were north face... google it holmes
Do you really need to talk on the phone while snowboarding that much?
Maybe it's to use the ipod or GPS apps?
But Burton and North Face both have liners that have the ability to control touchscreen devices. The Burton liner retails for about $18 and the North Face liner retails for $40. The Burton liner is very thin, while the North Face liner is a little thicker and can probably be used on spring days.