Share your experience!
I am completely exasperated with trying to solve this issue. I purchased a Z2, model 6503 only a year after purchasing a Z1, which I was very happy with. I purchased the Z2 solely because it is 4G LTE, which my Z1 was not. I signed up on Walmart's Family Mobile plan, which operates on T-Mobile's network. Come to find out, the Family Mobile plans were only 3G plans. Well, they recently added 4G to their plans and I quickly changed my plan. Very excited for the day to come when my plan would officially switch over to the 4G plan, I was very disappointed to still not be able to register on the 4G network. Every time I go to Mobile Networks, search, choose 4G Family Mobile, I get a could not register notice and the phone goes right back to the 3G network. I called Family Mobile and they said that the Sony phones have a different "signal" for their 4G LTE and it won't register on their 4G LTE network. They could have told me that before I switched, right? I went over to Metro Mobile to see about their plans and the guy there said that my phone is operating on 4G, even though I still only see an H in the notification area. He stated that HSPA IS 4G. Others all over the internet state it is not 4G. So, which is it and if it is 4G, why doesn't my phone show 4G? Lastly, if I go to T-Mobile and get on their "official" plan, which is $20 more than Family Mobile or Metro PCS, will I finally operate on 4G LTE? Please help before I destroy my phone with hard resets, software repairs, PC Companion as well as drive myself crazy being so obsessive about this! 
Hi,
If your phone is connected to 4G, it should say 4G or LTE. In order for 4G to work, the network provider you are using needs to use one or more of the frequency bands that the phone supports. If you are using the D6503 model of Xperia Z2, it supports the following bands:
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 20)
You should be able to get more information from your network provider about which bands they use.
The SIM-card also needs to be prepared for 4G, so you might need to order a new one for this. Also make sure that the network mode on your phone is set to 4G (preferred)/3G/GSM via Settings > More > Mobile networks > Network type.
@jmaxim917 The D6503 is the model that is adapted to the european market. This model will show 4G or LTE (depending on customization and/or software) if it have a connection to the 4G network.
I have the D6503 and here in Norway you need like Hampus is saying; a 4G ready SIM-card to get on the 4G network.
If not 4G SIM, the phone will only display H+.
With a 4G SIM, it displays 4G.
@jmaxim917: On my phone I have 4G(Preferred)/3G/GSM option weere on yours the same selection is called LTE(Preferred)/WDCMA/GSM.
In essence, they most likely show the same. (if not providers have "cheated")
4G and 3G is the often referred to as non-technical name for the different network types. The networktype-names displayed in the phone probably comes from customization done by operators. -Like I'm using the Nordic-variant of the Android-release, and it seems like this version likes to use the user-friendly term 3G and 4G instead of LTE, HDSPA/HDSPA+, WDCMA, etc, etc.
AT&T branded phones have their own customization, hence they can display whatever they want.
Of course there is a possibility for a carrier to let the phone show "LTE" but in real life it is still on a 3G/3G+ or less powwerfull technology.
In any case, without a 4G Sim, I get only H+.
Btw; When I'm in the US with my Z2, I can switch seemless/ad-hoc between many different providers/networks, that is impossible for the co-workers that have a phone "branded"/plan to for example AT&T, etc.:smileysmileywink:
Were you able to solve your issue or do you need more help, I'm in the US with AT&T