UPDATE to Ooma and my T Mobile HotSpot $10 a month

Just Decided to test this setup as a backup for 2 reasons:

1. IF I ever had a serious outage from regular internet, and T Mobile still going, I could still make and receive phone calls all over the house.
2. If I needed to take my Ooma on the road (to get calls to my home phone number, not a cell phone (which uses my phone minutes), I could do that with the Hot Spot. 

So, I repeated the setup for my T Mobile Hot Spot and IT WORKED!  It looks to use very little data.  Here are the stats on what it uses, so I probably don't need to switch it back and forth from my regular internet via router to the TMB Hotspot.

Ooma data usage
• A single call on a telo over iLBC at maximum redundancy uses up to 70 kbps in one direction.
• The iLBC codec with no redundancy uses about 35kbps or 4.375KB per sec each way.
• That's 525KB per minute of usage for both ways. 10 min call ~= 5.25MB usage. 60 min call ~= 31.5MB usage.

So, on my 2 gB HotSpot, I have never had it exceed that so shouldn't ever have to worry about it.  The HotSpot also just reduces my bandwidth speed when it reaches the 2 gB so hoping it will still support the phone.  Will be tracking the bandwidth use on the Hot Spot.  So, for $10 a month, away from home, I can run our cell phones (use Google Voice) or home phones using Ooma and a regular corded handset if I chose--for business away from home, etc.