Iphone 4 or Iphone 5 for talk time?

Stick with the iPhone 4. It has a longer talk time and the battery life for standby is about 75 hours longer.

If there were other reasons to upgrade, the iPhone 5 is worth the upgrade. They somehow made the screen bigger and the phone faster, but at the same, they made the phone extremely thinner and lighter. However, the weight if the iPhone 5 does not affects it's quality since it's made of glass and aluminum unlike the majority of smartphones which are made of plastic.

Since you are very much concerned about the talk time (not much particular with the other new features of Iphone technology), on my opinion, I would say, stick to your  Iphone 4. As I check the specs for Iphone 5, it can only provide you 480 minutes of talk time. I believe your Iphone 4 gives you almost 840 minutes for talk time.