You can buy an instant read thermometer for cheap. Use it until it breaks, then decide if you want an expensive one (I want a thermapen)

if it is a true fresh it will cook much faster than a previously frozen. Be careful, a lot of food markets defrost turkeys and claim they are fresh, or they were stored as partially frozen for several weeks before being sold as fresh. The processors can not kill enough fresh turkeys in the couple days before Thanksgiving, they are starting in October to provide "fresh" turkeys for Thanksgiving. There is fresh, then there is fresh!

Per the advice you've already received, it's the temperature that matters and not the time. Keep in mind as well that no two ovens are calibrated exactly identically. There could be a 25F degree difference between two ovens. A really good instant read thermometer is a very valuable tool to have. But also expensive. However you can use it for all types of meats and roasts.

Get an instant read thermometer. Cook to the temperature for best results. Those popups overcook it anyway. Just use timeline as a guide. from Martha Stewart
UNSTUFFED (time in hours)

4 to 6 lb breast..........1 1/2 to 2 1/4
6 to 8 lb breast..........2 1/4 to 3 1/4
8 to 12 lbs.......................2 3/4 to 3
12 to 14 lbs......................3 to 3 3/4
14 to 18 lbs................3 3/4 to 4 1/4
18 to 20 lbs................4 1/4 to 4 1/2
20 to 24 lbs......................4 1/2 to 5

STUFFED (time in hours)
8 to 12 lbs.......................3 to 3 1/2
12 to 14 lbs......................3 1/2 to 4
14 to 18 lbs......................4 to 4 1/4
18 to 20 lbs................4 1/4 to 4 3/4
20 to 24 lbs................4 3/4 to 5 1/4

Fresh will be juicier because it wasn't frozen. The cooking times should be about the same. Epicurious has a great chart for turkey doneness, taking into account turkey size, oven temp & time: http://bit.ly/dMQo7M But it's best to take the internal temperature too -- you'll want to hit at least 150 in the fleshy part of the thigh (the temp will continue to climb as it rests).