Is there no other way to enhance your voice signal as it is to expensive? Yes you can do three things.
Change your cellphone network settings so that it only communicates on GSM or 2G.
Move over to another Network provider with better signal or
Buy a signal band booster instead of dual or Tri band.
The following systems is just examples. A site visit is recommended to determine thickness of walls, the interior design, signal strenght available. Placement of boosters is critical