I live in the countryside where we have virtually no signal. One has to go outdoors to get anything. The least bad is Vodafone on which we get a marginal signal if standing next to a patio door, and that is why I recently moved to Voda (because nowadays a lot of people call your mobile # as a matter of course, rather than your home #) despite them being a lot more pricey than say T-M for a comparable product.
There are quite a few booster products around
e.g.
How well do these boosters work?
I tried the Vodafone Suresignal box, £50, which connects to Voda over a VPN. It didn't work. I found loads of posts all over the internet from people who could not it to work either.
Eventually I discovered (Voda's
business support is quite good these days) that it works as per the instructions only with a UPNP router, which nobody with any sense will be using. The box otherwise needs
five ports opened up in the router, plus some undocumented reconfig to give the box a fixed IP so you can port-forward to it. The open ports will of course be port-scanned and hammered by hackers almost immediately. I sent it back, so I am back to looking at boosters...
The problem is that (I assume the boosters need an outdoor aerial of some sort) even outdoors the signal is marginal - about 2 bars out of 5, on a Nokia phone.