那种便宜买手机两年合约不再有了(除了verizon existing customers)
现在有的options是：
1.全价买裸机: from $649
2. iphone upgrade program (all carriers?) from $32/month
3. carrier(看的at&t)： 有next every year ($27/month for 24 month installment) 和 next ($22/month for 30 month installment)
不太明白3的情况如果想中途terminate除了要付remaining手机的价值，还要付其他penalty吗？另外terminate时手机是不是就可以unlock了

本来是考虑1，用个便宜的month by month carrier, 找了一下发现at&t 现在$80 two lines, 3g data也不比那些month by month carrier贵多少。如果中途可以退出又没有除手机外附加penalty大概就 at&t next every year了。如果有好的prepaid carrier请推荐！


Update: 没想到大家讨论还挺积极，我来总结一下
1. 同样是unlocked phone, 4家major carrier在网络兼容性上有什么区别？
苹果官网的信息是这样的：
AT&T and T-Mobile

The iPhone for AT&T and T-Mobile does not support CDMA and will not work on Sprint or Verizon Wireless. It will use 3G cellular technology for voice services and either 3G or 4G LTE cellular technology for data services. However, the iPhone for AT&T and T-Mobile can roam internationally on many GSM carriers around the world.

Sprint and Verizon Wireless

If Sprint or Verizon Wireless is your wireless carrier, your iPhone will work on AT&T and T-Mobile once unlocked. An iPhone activated on Sprint or Verizon Wireless also has the ability to roam internationally on GSM networks.

International Roaming

All iPhone models are world phones, so you can use them almost anywhere. Which means you can roam internationally on GSM networks in over 200 countries around the world, whether you are a GSM or CDMA network customer. Availability of LTE data varies in some countries and depends on carrier support for certain LTE radio frequencies. For details on LTE network support, please see[url=http://apple.com/iphone/LTE]www.apple.com/iphone/LTE[/url]

这个很明确说了： 在美国国内verizon and sprint unlocked iphone 7可以用四个里面任何一个carrier, 但是att/t-mobile不可以用verizon/sprint做carrier

在中国的话，所有unlocked手机都可以使用，唯一的区别就是只有verizon/sprint的unlocked版本才可以使用中国三大运营商的LTE网络[url=http://apple.com/iphone/LTE]www.apple.com/iphone/LTE[/url] 我的理解是如果是att/t-mobile国内只能用2g/3g网络

2. 美国国内使用加入contract用哪个carrier?
今天4个carrier都宣布可以用iphone 6 and later models trade-in免费换iphone 7 32g。哪个划算真是只能根据当前手机plan具体分析，比如有的人用的grandfather family plan, like $20/line including data/voice, 那把iphone 6换出去拿个7每月还是这么点钱当然很爽。像我是att两年绑定的贵的要死的合同，怎么也得换新的plan, 如果不考虑carrier本地信号问题，跟哪家其实差不多

3. Prepaid no contract plan
这个搜了一下，简直多如牛毛，楼里有人推荐CtExcel 中国电信， $29/month, unlimited data and voice, 据说用tmobile网络
最近比较火的还有freedomPop 非常便宜，但是好像coverage不太reliable.


还有什么好的prepaid carrier请继续推荐我再来更新

没两年合同了？？？？？