The fact that most telcos in US offer cheaper prepaid plans with the same resources (unlimited voice/sms/data) than their 2-year-lock-in counterparts still surprises me... Is the lockin there really just to offset the price of the subsidized device?
If you're on a 2 year $100/month contract probably $30 a month goes to repay they phone cost the rest for the service insurance etc. If you don't upgrade straight away or get a big discount at the end of the contract you're effectively giving your mobile operator a massive profit jump.
I'm saying this because prepaid plans, in every other country I lived in, were absurdly expensive, if compared to the post-paid ones...