I'm keeping the microcell since I have several other family members and Friends and PIL who have AT&T phones but no iphones or wifi calling devices. I haven't really had any problems with the device in the past oh 3-4 years. For those who talk about "difficult to configure", I'm not really sure what they are referring to. I just had to plug it into my router (no DMZ required) and type the 1-2 device codes into my online account. At this point, one can do it with an iphone app I believe (that is what I use to quickly add friends that come by and need access - takes about a minute).
So, keeping it for now.
As far as WIFI calling, if an iphone sees the microcell it won't switch to WIFI. In places where I have good cell signal (even though WIFI is setup) like at work, it won't switch to WIFI until I get say in the elevator or sometimes in the parking garage. Places where the wifi is clearly stronger than the Cell signal