Micro Cell

Adding an additional Mcell to your home network can be done and others here have done so when a single Mcell doesn't cover their house due to its size or construction.

The additional Mcell should be located as far away as possible from the original Mcell to avoid RF interference.  Keep in mind that if you start a call on one Mcell and move around the house until you are out of range of it, your phone call will not handoff to the other Mcell and your call will drop.  Unfortunately, Mcells are not designed to work together like that, so be aware of this before going down that road.

@Avedis53 - thanks for the useful response to @dbrou53 question. I believe that 50' is the minimum that they should be separated but the further the better. If the OP has a WiFi-C (WiFi Calling) capable phone(s) then the MicroCell would not be needed at all.

Unfortunately, James's response from ATTCares, was useless, as usual.

@ James 

"This includes the usual manual on how to set this up."

If you'd actually read the manual, you would have seen that it does not refer to multiple Mcells at all, much less how to set them up.  If I were an AT&T employee posting here, I'd make sure I knew something about Mcells before posting a response and I'd certainly check my post for spelling and grammar errors.  You do get credit for addressing a post that we missed though.

@ dbrou53

The range of a Mcell is approximately a 45 foot diameter circle around the unit.  This can vary depending on walls, materials of construction, metal, electronic interference, etc...

The placement of multiple Mcells in the house will most likely require a little trial and error work to balance coverage with any potential interference between Mcells.