Recently while on holiday in the Glengarriff valley, west County Cork, I was faced with this problem.
At my location I was getting tantalizing brief connections to the cell network (Vodafone IE), and occasionally the odd GPRS IP packet might make it through. But nothing close to usable.
As a rule of thumb you can improve a weak radio signal by raising the height of the antenna. So I got several planks of wood. Strapped them together with duct tape to form a make shift antenna mast about 8m in height. I switched the mobile hotspot feature on, taped the phone to the top of the mast and raised it.
And sure enough I was able to get a usable [*] connection where none existed before.
[*] The connection was only GPRS and there was still packet loss... but sufficient to get email in and out. Perhaps another few meters might have made the difference.