I did some checking and this is what we use
Amazon.com: zBoost YX-510 Cell Phone Signal Booster Dual-Band Unit for Home or Office: Cell Phones & Accessories
Our setup ended up costing around $500-$700 because we used two high gain (not the standard) antannea and pointed them at the appropriate carriers' towers.
It works very well.
We've used things like that at job sites before and they worked really well :smile: