The iPhone 4S becomes available Friday, and if you're thinking of upgrading to the new model it might be wise to act fast. With pre-orders for the 4S rolling in at a record high, many are trying to get rid of their iPhone 4 at used electronics stores and websites. Little did they expect, what they'll receive in cash back is dropping faster. If at all, the time to sell is probably now.

A popular trade-in site called NextWorth is already reporting that prices for the 16 GB have dropped from $250 at the start of October to $200 right now. The same price reduction is happening with another seller called Gazelle.

Although resale prices are likely to continue dropping, some people are holding off until they get a feel for the new 4S. They might not be wrong to play it safe right now. After all, there have already been talks of bugs and problems with the iOS 5 on the 4S.

Still, Apple itself continues to sell the 3GS after all this time. That's because they know there exists a market for economical people who want an iPhone too. The iPhone 4 is soon to be old news with how quickly smartphones upgrade these days, but, if Apple's taught us anything, it's that there will always be people who want in on the trend for cheap.