If you think that the bigger capacity of the iPhone 4 (as compared to iPhone 3Gs) still cannot satisfy your desire for longer talktime, maybe this Exolife casing from ExoGear can help you.
If you think that the bigger capacity of the iPhone 4 (as compared to iPhone 3Gs) still cannot satisfy your desire for longer talktime, maybe this Exolife casing from ExoGear can help you.