中国有3家，美国其实也只有4家，另外还有一些Local，只能在当地用，可以忽略，还有一些实际上是虚拟运营商，没有自己的网络，租用的都是4大的。1.VerizonCDMA：850MHz，1900MHzCDMA EVDO/CDMA2000(3G):850MHz，1900MHzLTE(FDD):700MHz(Band 13)，1700Mhz(Band 4)2.SprintCDMA:800MHz(Band 10),1900MHz(Band 2)CDMA EVDO/CDMA2000(3G):1900MHz(Band 2)LTE(FDD):800MHz(Band 26)，1900MHz(优先,Band 25)WiMAX(已终止):2500MHzLTE(TDD):2500MHz(Band 41)3.T-MobileGSM:1900MHz，850MHzWCDMA(3G，HSPA+):1700/2100MHz(成对)，1900MhzCDMA EVDO/CDMA2000(3G)：1700/2100MHz(成对，优先)，1900MHzLTE(FDD):1700/2100MHz(成对，优先，band 4)
4.AT&TGSM:850MHz，1900MHz(个别地区)WCDMA(3G，HSPA+):1900MHz(优先),850MHzLTE(FDD):1700MHz/2100MHz(成对，优先,band 4)，1900MHz(Band 2)，700MHz(Band 17,29)
在国内买的手机要在美国使用，需要仔细看说明，以T-Mobile为例：
2G(图标显示E)：T-Mobile's GSM network operates in 850 MHz and 1900 MHz frequencies.A device is only able to use 850 MHz or 1900 MHz, it can still use T-Mobile's domestic network.
3G(图标显示3G)：T-Mobile's UMTS network operates in Band IV, which uses 1700 MHz and 2100 MHz frequencies. Specifically, T-Mobile uses the 1700 MHz frequency to send information to cell sites and then uses the 2100 MHz frequency to receive information. A device must be able to use both frequencies to use T-Mobile's domestic UMTS network.
4G(图标显示H+)：T-Mobile's HSPA+ network operates on the same band as our 3G network, Band IV, which uses 1700 MHz and 2100 MHz frequencies to transmit voice and data services. The 1700 MHz frequency sends information to cell sites and the 2100 MHz frequency receives information.T-Mobile is switching some 1900 MHz frequency from EDGE to HSPA+. This will allow devices that work on 1900 MHz, such as AT&T devices, to use our 4G network.
4G LTE(真正的4G):T-Mobile’s 4G LTE network will operate on the same band as our 4G HSPA+ network, Band IV, which uses 1700 MHz and 2100 MHz frequencies to transmit data services.4G LTE does not carry voice services, so calls will fall back to our HSPA+ network until voice over LTE (VoLTE) software is ready.T-Mobile’s 4G LTE equipment will be the newest and most up-to-date of any carrier.
Ultra.me公司：For voice and text, you need a tri-band or quad-band phone that supports either the 850mhz or 1900mhz frequency.Phones that support 1900mhz will get data from us at 3/4G speeds in most of our coverage areas.
由于CDMA模式的手机很多不是机卡分离的，因此，国内人到美国大部分使用AT&T和T-Mobile的网络（有一个例外，中国电信漫游到美国，4个公司的信号都可以使用，前两个信号好一些，后两个差一些，漫游费用也不一致），到美国后需要的手机（GSM/WCDMA）是这样的：
基本通话：3频及以上（900M,1800M,1900M,850M）上网：除了以上
WCDMA(UMTS,HSPA+)：除了国内所用的2100M（联通，Band1），要求至少一个1900M(Band2)，最好还要有1700M(Band4)
FDD LTE：Band4(首选，甚至是必须的)，Band2(1900M)，Band5(850M)
美国的LTE频段有10个，分别为LTE:Bands:1/2/4/5/17/19/25/26/41