What would happen if you took a smartphone out in a space walk while being turned on?

Some comments on other answers, suspect vacuum and coldness of space to have negative effects of the integrity of the phone. I doubt they do.

Why would the vacuum be bad? There isn't any atmosphere crushing down on an evacuated phone. There are also no phone parts which need air to work. The only possible damage could occur if there are parts containing air which might expand. There might be some air trapped in the probably airtight space between the lens and camera sensor which could expand in the vacuum and damage the camera.

The low temperature in space needs to reach the phone. Since there are no particles to conduct the heat or lack thereof it might not be a big issue. Maybe it is even the other way around. Heat generated by the phone would not conduct away to surrounding air and could only radiate off. This might not be enough and the phone could overheat.

The above are just speculations but I'd like to know if they are wrong or make sense.
Other things, which are obvious, would be the lack of sound traveling through the vacuum of space as well as as the connectivity issues. Make sure there are some off line games installed before your trip and that your glove is touch screen enabled. ;-)

The GPS should work if you are stationary with regards to the planet. However if you travel faster then it comes down to how often your GPS aquires its position and how fast it is displayed. It might be that by the time you see the information on your phone you'd be already 5 miles away from your previous location. Thats how far you would travel within a second at 17000mph.