Hi, yes the 659 could be re deployed as a WAP, however its wireless performance is not that flash, that said, just disable the DHCP on the 659, allocate the lan IP address to one within your new network and connect to it via one of its LAN ports, nothing connects to it WAN.
As for the edge router, when configuring you configure one of the ethernet ports (typically eth0 but any will do) as the WAN and one as LAN, you could configure the remainder into a brdige switch and therefore treat them as a lan switch.
As for phone sockets, are you using those currently, if on Spark then I doubt it.
Cyril