What you're looking for if you want your own sims is a picocell, like
http://www.mobilecomms-technology.co...ing/ip_access/
But as others have mentioned, it is regulated. In the UK a batch of licenses for these were issued last year, lots of universities and large companies are starting to set up their own mini-networks on their campuses.
You'll also need a roaming provider if you then want seamless roaming outside your local picocell, wire9.com is one of the UK providers of this.
Maybe something more suitable would be an amplifier/repeater, it it's just to fix bad reception? Like this:
http://www.criterioncellular.com/rep...peater-SR.html
(us version, but there's probably something similar in Europe)