Hi james-richter,
You're in uncharted and unsupported territories.... :-)
I don't know anything about the Cisco 3640, but if you can get its FXO ports to register to the SPA9000, you should be able to get it to work.
Run the SPA9000 in debug level 3 mode and run the related SPA9000 line in Full debug mode so you will have an idea of what is going on:
https://www.myciscocommunity.com/docs/DOC-3032
The SPA9000 web-ui Admin Guide should prove useful in your quest:
SPA9000 web-ui: http://www.cisco.com/en/US/docs/voice_ip_comm/csbpvs/spa9000/installation/guide/spa9000_voice_system_webui_ig.pdf
Good luck,
Patrick
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