I spotted on of these devices a while ago - it plugs into a broadband connection and effectively sets up a mini 3G cell - the box connects to a Vodafone server and your 3G telephone connects to the box. It gives me a 5 bar signal at home and works for both voice and data calls.
It takes a few minutes to set up and about ten minutes to come up as service ready, but then you are done. It works a treat and costs around £50 as a one off payment. Calls and connections are as per your contract, so once you have purchased the box, there are no additional costs. In fact, I had to swap from O2 (my current phone provider) to Vodafone and purchased the box as part of the transfer. It cost £20 as a one off payment.
Unfortunately, O2 did not offer a similar service, so after more than 15 years on O2 (I started out on CellNet), I had to change mobile providers to get a decent signal at home.
Poor information here: http://www.vodafone.co.uk/suresignal
