LTE is confusingly often associated with the term 4G (including here). In reality, the 4G standard is one that hasn't quite been reached yet - that would require speeds of 1 Gb/s, about ten times faster than current LTE networks. The proliferation of the term is unfortunate, but until true 4G networks are available then you can just take the two terms to be synonymous in practice.
But 3Mbps to 10Mbps is the average. If you’re really lucky you might top 20Mbps using a 4G network on your smartphone.
LTE provides the fastest data network connection at the present time. LTE is faster than many home broadband connections, and as such allows for rapid downloads, streaming of Full HD videos or music, and very rapid page loads.
Different 4G bands/spectrums: There are different bands of 4G, and it all gets quite complicated. 2.6GHz 4G is the fastest, followed by 1.8GHz and 800MHz. While 800MHz doesn’t boast the same data capacity as the faster 4G bands it is better at traveling over longer distances and also at penetrating walls so provides better signal when indoors
H - HSDPA (High Speed Downlink Packet Access)
HSDPA is a slightly slower version of HSDPA+, offering data speeds of around 7.2 Mb/s. This is about the minimum speed for reliable streaming video content at HD resolution, and still offers pretty good web surfing and music streaming.
3G - 3rd Generation (aka UMTS)
The 3G standard uses a technology called UMTS (Universal Mobile Telecommunications System) as its core network architecture. It first saw the light of day in 2001. This network combines aspects of the 2G network with some new technologies and protocols to deliver a significantly faster data rate.
It was so amazingly fast that Apple bolted the name onto its iPhone, so we have the iPhone 3G and later 3GS. 3G data networks were the first to support video calling with download speeds of up to 2 Mb/s (although initially speeds of only 384 Kb/s were supported). There’s another brand of 3G called HPSA, that’s sometimes dubbed 3.5G, which boasts potential speeds of between 600Kbps and a whopping 10Mbps, although the average is 1-3Mbps.
It was at this stage that mobile internet got decent, and we saw an explosion of new capabilities for mobile phones in the early 2000s (like email, vis a vis BlackBerry).
E - EDGE (Enhanced Data Rates for GSM Evolution)
The E stands for EDGE (Enhanced Data rates for GSM Evolution). This is a step up from GPRS and can reach speeds between 120Kbps to 384Kbps. This was the original iPhone’s top data network speed. Now it’s met with a sigh because it means where you’re standing doesn’t have a 3G or 4G signal.
EDGE can be thought of as 2.75G, offering speeds of up to 384 kb/s. EDGE was developed as a cheap way for carriers to upgrade their 2G networks to nearly 3G speeds, without needing to build all-new infrastructure. EDGE is relatively uncommon now worldwide, but you do get it from time to time and it's generally enough to look something up if you have the patience. Interestingly, this means that EDGE came after 3G even though it's a slower standard.
Still, it’s better than GPRS, eh!
G - GPRS (General Packet Radio Service)
One step up from no data signal at all is GPRS, which stands for General Packet Radio Service. Wikipedia defines GPRS as a “best effort” service and “a packet oriented mobile data service on the 2G and 3G cellular communication system's Global System for Mobile communications (GSM).”
GPRS is a little faster than the earlier GSM standard which first popularized data connections. Depending on who you believe in 2G systems GPRS provides data rates of 35–171Kilobits per second (Kbps). 2G cellular technology combined with GPRS is sometimes described as 2.5G. It provides slow-speed data transfer, by using unused time division multiple access (TDMA) channels in, for example, the GSM system.
All you need to know is that GPRS means you might eventually get a webpage to load or an email to send, but it will probably take longer than you have the patience for (if you have a consistent connection).
This was the first "always-on" data service and the oldest one that you'll connect to using an Android, iOS or Windows Phone. While older networks exist, you aren't likely to come across them these days and it's best left for the historically minded.