Uniden multi handset system with bluetooth Cellink on sale at Sears.
Uniden DECT 6.0 Bluetooth Cordless Phone System with Digital Answering System $49.99, regular price is $79.99
Sears Item# 00329741000 | Model# D3280-2
http://www.sears.com/shc/s/p_10153_12605_SP100A2775S3070899402P?prdNo=6&blockNo=6&blockType=G6
Uniden product page
http://www.uniden.com/bluetooth-phones/dect-60-cordless-phone-with-digital-answerer-celllink+153-bluetooth+reg-connection/invt/d32802g/
Expandable to up to 12 handsets. If you need more handsets this is the cheapest way to get them. You can buy multiples of this product and use the handsets with one of the bases, or an existing system if you have one. Once you unregister the handsets from the base, you can register them to another base. Then the base/answering machine acts like a charger only.
Other Uniden systems allow you to register the handsets to multiple bases for use on multi-line systems
there is a refurb 6 handset Panasonic brand system on ebay for $99.99
Search for item # 260853572887