The SPA9000 Analog IP PBX solution consist of a new configuration
option which allows the SPA9000 to serve a Small Business with up to
18 Analog Phones, but using all benefits the benefits of VoIP. It is
an Easy to deploy and affordable solution with a standard PBX feature
set. It is designed for those Small Businesses with a reduced budget
requiring basic telephony features, willing to use the savings of VoIP
or to replace the cost of individual land lines with a VoIP-based
affordable solution.
https://www.myciscocommunity.com/docs/DOC-2192