At least for AT&T and Verizon, the bills are a little lower now if you have an unsubsidized device. Before the Next/ Edge programs came out (and in the early days of the programs) there was no discount for paying off a subsidy.
But I noticed that most of the plans that allow unsubsidized phones for a lower cost are higher end plans anyway. I still have an old plan of 450 minutes. 200 text messages. And 3GB of data. With FAN discount, about $73/month. ATT Mobile Value plan (2GB, unlimited text/talk) would cost about $65/month if I bring my phone. Adjust for discount and taxes. So, over 2 years it would save me maybe $240 if I didn't plan to buy another phone in that time. But since average discount is $450+ tax, and what with iMessage and M2M calls, I don't need the unlimited talk/text, it would personally cost me more. So I may as well keep my existing plan. Which you can't get the text plan anymore anyway.
If I was to go to one of the pre-paid services like ST, for around $45/month, it would save me a little money.
The downside of my existing contract is that, if I DIDN'T want to upgrade after 2 years, the rate doesn't go down. But last time I upgraded, I gave my phone to my brother-in-law who uses ST for free. When I upgrade this fall, I'll give my phone to someone else. So it isn't like it is going into a drawer like my old Palm Treo.
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Looking at the news reports about the differences between the 2 houses bills before it was reconciled was that the senate one allowed bulk unlocking. Which has 2 main usages. One, places that accept donations of phones might want to unlock them to make them more usable for more people. The other is for people who buy them with the intent of selling them in other countries (gray markets). Companies establish distribution agreements in other countries to sell phones officially in different markets. What with currency fluctuations, it can lead to phones being priced higher in a market than the international price. Just from published reports of prices, it can be hard to tell whether the listed price is gauging. Or high import tariffs. VATs. Or just fluctuations.
And of course published prices in the US don't normally include the sales taxes. Which has to be factored in when comparing prices.