I would like to build a closed system where I can send faxes and make calls over a distance of around 500m.  I've done a bit of research and I think the best way to do it would be with an Analogue Telephone Adapter, like such:

http://www.cisco.com/en/US/docs/voice_ip_comm/cata/186_188/2_15/english/administration/guide/sip/SIP88CH1.html

At each end I would like a bank of 2-3 fax machines and 2-3 phones.  The above device will do a total of 2 phones or faxs.  Any ideas on how I could expand on this number?  Could I run cat5 from one router to another and have multiple ATA's off each router?

Any input would be greatly appreciated.