All You Need To Know about 4G Cell Phones

What is 4G?

4G (4th Generation) has been used in a couple of different contexts:

(1) 4G cellular network – a cellular communication network at the 4G standard, including using mobile IP for addressing and reaching a minimal data communication throughput (speed), etc.

(2) 4G-quality wireless data service – data service provided by a wireless carrier that reaches minimal 4G speed. In reality, it could be run on top of a 4G wireless network or an upgraded version of a 3G network (for example HSPA+). Many early carrier-branded 4G services were actually run on 3G networks.

(3) 4G cellphone – a cellphone that supports 4G cellular network’s data communication standards. They are typically smart phones by default as well.


2G, 3G, 4G Network Data Speed Comparsion (estimates)















Downlink (bps)







Uplink (bps)







LTE and 4G

LTE is an abbreviation of the technology currently used by (almost) all global 4G cellular networks. If it’s irrelevant, then don’t mention it, and last sentence is redundant.

In theory, LTE is faster than 4G services run on top of 3G networks, but one should keep in mind that the actual speed also depends on other factors including how many people are concurrently using the data network within a small area. It’s a summary within a summary


Can a phone be used for my 4G carrier?

For all unlocked phones - (phones not locked by a particular carrier, 3 major factors determine whether a phone can be used for a particular carrier:

(1) Variations of LTE technology. There are 2 variations of LTE technology: FDD LTE (or FD-LTE) and TDD LTE (or TD-LTE), most of which share technology but also have differences. Most carriers use only one. Some phones support one and some phones support both.

(2) Frequency band matching with your carrier. Globally there are around 40 different frequency bands (referred by numerical numbers in the 4G standard) supporting 4G wireless communications, and each carrier only uses a small subset of bands and all phones only support a subset of bands as well. So Yyour phone’s supported bands have to have overlap with the carrier band to get on the carrier’s network. In the same country, different carriers may share 4G bands or may not share 4G bands, so matching bands between phone and carrier is key; not between phone and countries. Some phone manufacturers provide a different SKU for different geo markets for the same phone model, for instance, a European version v.s. a North America version, but it only means the SKU’s bands are optimized to support as many carriers as possible for this particular market, and there is no guarantee that the SKU would support all carriers in this market.

(3) Whether your carrier allows unlocked phones to register into its network. In the past, some carriers ,(such as Verizon,) had restrictions that did not allow unlocked phones to sign into its network, but no such restrictions exist today with carriers.


3G and 2G backwards competibility

This issue should be less and less of a concern over time as the 4G signal coverage is quickly increasing globally. In general, the world had 3 camps for 2G and 3G era: (1) GSM + WCDMA + upgrades such as HSPA, (2) CDMAOne + CDMA2000 + its upgrades (mainly Verizon, Sprint in US, KDDI in Japan, China Telecom), and (3) GSM + TD-SCDMA (China Mobile only). So unless you are with Verizon, Sprint, or China Mobile, your 4G phone would have full backwards compatibility with 2G and 3G technology platforms. However, it has a frequency band matching issue, just like in 4G. In general, most 4G phones would cover all 2G bands for global usage but it may not cover the right 3G band with your carrier’s 3G network.

Please check additional resources for all CDMA2000 networks in the world.


Voice phone calls in 4G

When you are making a voice phone call with your 4G phone today, most likely you are using the 2G or 3G network to do so. The good news is that this means you can access the data network and surf the Internet while you are making a phone call, but it also means that if the phone does not support your carrier’s 2G and 3G network, you may not be able to make voice phone calls at all. Many carriers are working on their Voice Over LTE (VoLTE) solutions to allow customers to make (high definition) voice phone calls with its 4G data network directly and have plans to retire their 2G networks in the next couple of years. But as of 2017, the world’s VoLTE offerings are still limited.  



LTE Advanced & LTE Advanced Pro - both are upgrades of LTE network to provide better speed, and sometimes referred as 4.5G and 4.75G. Some phones and carriers are now supporting LTE Advanced, but LTE Advanced Pro is still in development and implementation phase.


Device Category

Device category defines the max data transmitting speed of a device. Only when the device’s max data speed is high, can it fully leverage a fast 4G network’s data pipe. Ideally a customer should not need to know anything about the device category, and the phone manufacturer or seller should simply provide the max data transmitting speed as part of the phone specification, including both downlink (download speed) and uplink (upload speed).

SIM Card Size

SIM card size is not a 4G issue, but it could confuse a customer when he/she chooses a cellphone. Typically a phone only supports one or two SIM card sizes, and you should be able to order a SIM card from your carrier to match your phone SIM slot size easily.

Optional Advanced Topics

(1) FDD LTE and TDD LTE mixture - very rarely, some carriers may introduce a service that leverages both technology platforms, such as Sprint’ Spark service, to optimize network efficiency in both city and countryside. In this case, if your phone supports one technology, it should work.

(2) LTE was not originally 4G! At first, LTE didn’t meet 4G requirements, but it qualified later on.

(3) HSPA+ is an upgrade of WCDMA network, and should be more properly called 3.9G, but many times marketed as 4G by carriers.

(4) XLTE: simply Version’s marketing name for its LTE offering. X means nothing here.

(5) Communication Speed v.s. Data Storage Size - when you read the communication speed/max throughput is 100M, it actually means 100M bits per second, while a data storage size of a 100M file actually means 100M bytes. And 1 byte = 8 bits. This is part of the reason why a network may not feel as fast as the labeled speed.


Additional Resources

All CDMA2000 3G networks in the world: