Just thought I'd post a couple things here since I've had experience on this recently. I have 2 Network Extenders (2 buildings) and mine are the original 1X version. After the Advance Calling update, a curious thing started happening. After a couple months I noticed my bills started going up in price. I went to look at them to see who on our share plan was running up the minutes (still on a grandfathered UDP). The problem was on my line. Almost every call I made had a duplicate call happening at the same time to multiple number with the same Texas area code. I called Verizon and we started a ticket on it. Between my investigating and theirs, we found out that the NE doesn't play nice with AC. Every time a call was placed when connected to my NE with AC turned on, those duplicate calls to Texas were placed, which meant that all of my calls that shoulve been free (M2M, nights & weekends, and friends & family) were being counted against our allotment, and any peak calls were double charged. Verizon said it was working on the issue, and a latch was planned for mid April, so I was instructed to leave AC off until they contacted me. However I haven't heard from them yet, so I don't know if the issue is fixed or not. Since I don't know what kind of plan you're on, I can't say if this will affect you or not (if you have unlimited minutes it shouldn't affect your bill, but if you're on an older an with a limited amount of minutes, it will). So it might be a good idea to check before you use the NE too much.
As to Doogald's question, they don't currently have an LTE Network Extender available, and depending which tech I talked too, there may not ever be one. The first level 2 tech I talked too during the above issue told me that an LTE NE would be available by mid 2015. The next one I talked to said they weren't doing an LTE NE and were going to instead use WiFi calling to make up for the lack of signal. So I don't know for sure, I think I'd prefer WiFi calling rather than having extra pieces of gear that also use up my ISP connection like my NE does. At least then it would only use the connection during a call. But I'd imagine that would mean no VoLTE HD calling with WiFi, but I'm not entirely sure about that. I also don't know if WiFi calling will work with any WiFi router or if it needs a specific model.