4G has been put into commercial use for some time. There little difference among of three domestic operators 4G use. For example, China Unicom mainly use TDD LTE technology, and Telecom and China Unicom mainly apply FDD LTE technology.
Currently there are three main 4G voice solutions: Dual standby, CSFB（Circuit Switched Fallback) and VoLTE(Voice over LTE)
1. Dual standby: dual standby refers to 4G and 3G / 2G standby at the same time. 4G is for Internet use, 3G/2G is for phone. The technology inside the phone has two radio frequency transmission system. This will cost much battery.
2.CSFB: CSFB is one kind of model that the internet will down to 2G mode during calling (no Internet access). It will recover to 4G/3G condition. This technique uses only one set of radio frequency chips. Now 4G test is primarily applied to test this program, after all, the 4G network is still under construction and there are some areas not yet complete 4G coverage. Thus, internet model switch is very important. Apple A1533 telecommunications technology also called the SRLTE is a special form of CSFB.At home, you can even use DINGLI Samsung and Sony Ericsson mobile phones to test. Many projects carried out experience testing directly on IPHONE5S. In foreign countries, TEMS is rarely used for testing while NEMO is mostly applied.
3.VoLTE：this technology is very useful which is one kind of voice solutions bearing on 4g internet under the condition of the whole IP end-to-end speech. It has improved much in access delay. It is also a promising technology for 4g is an irresistible trend.
4. Strictly speaking, LTE internet is just data network. before realizing VOLTE, LTE can only be called 3.5G, or defect 4G. 4G internet refers to the internet with perfect voice solution and does not rely on 2/3G internet since voice is an important part to data.