Check out CDMA amplifiers....there are many different solutions out there.
For example -
http://www.phonemerchants.com/poda3wadubac.html
Sprint also offers something called an AIRAVE - which essentially plugs into your broadband to create a CDMA hotspot...not sure if alltel has a similar product.
http://www.nextel.com/en/services/airave/index.shtml