I have an iphone 6 on Verizon. Ever since doing the 8.1 update it says Extended at the top of the screen where it normally says Verizon. I saw a couple of threads about this on the Apple Discussion forums so I know I'm not the only one with this problem.
After two days on the phone with Verizon (Vzw) tier 2 support and Apple support I was able to get an answer, and get this fixed. There are some known issues with the Vzw iPhones staying in extended mode - so check these first! This is a very important issue to get fixed because until you do you are stuck on other cell operators towers and not Vzw and you will not get high definition calling!
1) IMPORTANT- If you are using a Vzw Network Extender in your home or office, since update of ios 8.1 you will always see extended mode on your phone, no matter what, for now. (4g HD calling not yet available through Vpn tunnel)
2) 8.1 apple update defaulted all the iPhone cellular mode LTE setting to data only. to fix, go to settings> Cellular > Enable LTE > Select Voice & Data. a check mark should appear withing 30 seconds and Verizon will reappear on iPhone. If the check mark appears you are now back on Vzw cell network and have High Def calling. If not - complete a "hard reset on the iPhone" Do this by holding down your power button and home button until you see the apple logo on the screen, This actually disconnects the batter on the phone and forces the sim card to reach out to the towers and reinitialize settings.
If this does not work, toggle on and off Airplane Mode
If that does not work; go to settings> General> Reset> Reset Network Settings
Now if after all that your check mark does not appear or you get a pop box on the phone that says "call Vzw to enable LTE calls" then here is the solution:
Call Vzw, have them add the following 3 codes on your account:
A) Advanced Calling 1.0 - Vzw Feature Code 81143
B) High Def Voice - Vzw Feature Code 81158
C) High Def Access - Vzw Feature Code 81186
If you give the Vzw rep the three feature codes it will make your life easier because this is a very new issue!
Now you can hard reset and select LTE Voice and Data and get back on the Vzw Network
2 days and 4 hours on the phone with both companies solved this issue, I am not that smart, just pushy to get my new HD calling that I bought the dam iPhone 6 for! Cheers! gene
Note: When doing all this you must be in good range of a Vzw cell tower and have at least two bars of signal on your phone, if not go outside.