The iPhone 5 has created a lot of excitement among buyers, but I’m excited about it for a different reason.

For me, it’s all about the spin-off effect of all those people who will want to dump their iPhone 4 or 4S or an even older model now. Amazon is offering Amazon gift cards if you trade in a fully functional iPhone. They’re paying $85 in gift cards for the iPhone 3, and up to $400 for a well-preserved iPhone 4S.

The marketplace value of a used iPhone is high enough to cover a contract break fee with one wireless carrier so you can go to another and keep your number. This is your chance to exit from AT&T for iPhone service that is too costly and too unreliable.

For a really Clark Smart move, you can take an older unlocked iPhone to a no-contract carrier and lower your monthly costs by about 50 percent. For example, you can buy a SIM card from Straight Talk and use an unlocked iPhone on their network for $45 a month, with the service being provided by T-Mobile or AT&T. Visit StraightTalk.com for more details.

Meanwhile, Cricket will sell you an iPhone 5 at the unsubsidized price of $499 instead of the subsidized $199 charged by the bigger wireless carriers. The cost of monthly service on Cricket is $55. For that price, you get unlimited calling, unlimited texting and 2.5 GB of data, all with no contract. So you have a higher cost upfront for the phone, but it’s overcome by cheaper monthly service. Visit myCricket.com for more details.

Straight Talk also has a fancy Galaxy S for $349 with unlimited service for $45 a month. That’s a fraction of what the big guys charge, and it’s also no contract. Best of all, it is run behind the scenes on the Verizon network at half the cost of branded Verizon service.