Here in France, you have choice, and you can save money if you keep your old phone.
You don't have to buy a new phone each 2 years if it's not broken. That's why, if you keep your old phone and switch carrier, you can have plan for unlimited calls/SMS and 3go data for 20/month or less.
You can switch carrier when you want with this kind of plan, you are free, So you can even find cheaper plan with only 2hours call and unlimited sms for 2 or 3 per month (without data, not good for an iPhone.
If you want to change your phone, you have to go back to "jail" for two years with a 60/month for 2 or 3 hours calls, or buy a 600 phone. That's why here, most of us keep our old working 3GS/4/4S after two years, switch carrier and don't buy the new one! All people i know do that....
Plus, iPhone5 is actually not ready for 4G in France...this is the second reason for me not to change.