Microcell

The Mcell is a 3G device only.  It will connect to 4G devices but at 3G speeds only.

Which smart phones do you have?  If they are WiFi Calling capable, you should use WiFi-C instead of a Mcell.

I'm confused.  You said you get good WiFi everywhere in the house but then indicate no internet in the basement.  Does that mean you get no WiFi signal in the basement?

Where is your router located?

@Heltons  If you have no wifi signal in your basement, the microcell isn't going to help.  It uses your wifi to provide talk and text.  For a Microcell (or wifi calling) to work, you would have to reconfigure your wifi network to cover the basement.   

Its not unusual for signal to be blocked under ground level.  

@Heltons - as mentioned above, WiFi has nothing to do with the MicroCell being as it broadcasts a 3G signal only. If you have no WiFi in the basement, then you won't be able to do WiFi-C (WiFi Calling) if your phone(s) are capable of that. You may be able to get away with an access point to connect to a MicroCell for 3G but you'd have to figure out how to configure that yourself depending on your hardware.

Please explain your setup in a little more detail (hardware, models of phone, ISP, etc).

One suggestion is to use a power line adapter for the basement.  Do not know how good a power line adapter will work for voice if the phone has wifi calling  Netgear has several or you could use another manufacture.  Saw some in Best Buy or you can go to Amazon.com and get a better price. 

http://netgear.com/home/products/networking/powerline/

@Fl_retire - we don't normally recommend powerline adapters because there can be all kinds of issues depending on how the house is wired, outlets grounded, etc. VoIP is very touchy about it's connection and any extraneous noise on the line, while it may not affect internet traffic, it can and will affect voice quality.

@lizdance40 

The Mcell does not use WiFi to provide talk and/or text.  It connects directly to a router/gateway via Ethernet cable.  One doesn't need WiFi at all to operate a Mcell, just a modem connected to the internet.  I think you're confusing WiFi-C with the Mcell.

Certainly, no WiFi in the basement means no WiFi-C unless the OP relocates their router/gateway to cover the basement or adds a range extender/access point to provide the coverage.

@Heltons

I've done both the range extender and the Powerline adapter game with the Mcell to provide better coverage in my home and both can increase the unreliability of the Mcell.  Transmitting a digital signal across your home's alternating current wiring is easily interfered with by AC ground loops, passing the signal cross-phase or cross-breaker or by interference from other electrical devices in your home like a refrigerator, microwave oven or even something as simple as a GFCI outlet.  I have a pair of Netgear  Powerline 200 mbps Nano adapters I'll sell you for cheap if you want to try it but understand your home AC wiring system needs to be pristine in order for them to work.  My home AC wiring is not pristine and the Mcell would continually lose its connection to the AT&T servers because of electrical interference.

I had better luck with a range extender(access point) to better centrally locate my Mcell to provide coverage over our 4-level, 4000 sq. ft. house (router in basement) but the range extender had to wirelessly connect the Mcell to the router, adding another layer of complexity to my home network that proved to be less reliable than desired.

Ultimately, I went to WiFi Calling after replacing our phones with appropriate WiFi-C phones and my problems went away, even with using a range extender on our home network. 

We've asked you for additional information about your phones and home network.  Please provide that in order for us to offer advice.