USGA to Allow GPS Rangerinders
Oct
3
2005
This week the US Golf Association (USGA) announced that it will leave the issue of electronic rangerinders, including GPS rangefinders, up to the discretion of local rules. Therefore individual course managers will be able to decide for themselves if such devices will be allowed in competitions. The PGA has not made such a ruling and GPS range finders are still not allowed for those events.
I doubt even a range finder would help my game. 
Now that many cellphones have gps capabilities, such as the iPhone, I know you are going to see some great ways to get distance to the green via a cellphone, instead of through a separate golf gps device.
And I’m sure you just happen to know of such a tool, aye?
Softwares are available. But this has been tried and failed for three reasons:- 1)PDA screens are not designed to be viewed under direct sunlight; 2) PDAs (most) are not water- (playing in rain)and sport-proof (slipping it from your sweaty palms); 3) Fumbling with numerous buttons and navigation keys or stylus on PDA is the LAST thing you want to do before a shot, and 4) PDAs (iPhones etc) are much more vulnerable to theft than golf specific handheld units (also losing your PDA along with the zillion of valuable info on it spells migrain).