If you are able to keep your current device until summer, do it. There will be a new iPhone during the summer. It may not be a completely new and unique device, but it will be an upgrade from the current one. 🙂
There have been probably over 20 threads on this subject. It's been beaten into the ground. Phil said during Macworld that the product cycle for the iPhone is every June/July. Beyond that statement, there is no other solid information.