Verizon sells signal boosters, I would guess most others do also. there are also several generic signal booster providers. Wilson seems to have the most options.
http://powerfulsignal.com/wilson-mo...xBBHhRGBYZUo9cq7ruONo4pa731PmMFH-caAgk18P8HAQ
http://powerfulsignal.com/wilson-mo...xBBHhRGBYZUo9cq7ruONo4pa731PmMFH-caAgk18P8HAQ