What is the reason for you to choose iPhone 4 or iPhone 4s?

Cost and features. You need to weigh the increased cost of the 4s against the increased cost. If you believe you will use the added voice features then go with the 4s if not then the 4 seems to be a better deal.With new models coming out on a yearly basis you may want to go with the newer phone because there seems to be a major feature or service new each year and with most subsidized phones on two year contracts, starting with the latest model may give a better value over the two year contract.