Background
Spectralink 8020 wifi phones work well with Sipx. Sipx 4.2.1 and later require a version of 8020 firmware that as of 5/19/11 is not available without out calling Polycom support. It will then be provided free of charge. They want to track who all is using, but do plan to make it publicly available with their next firmware release.
Upgrading Fimrware
pd14csi.bin - 201.104
pd14odsi.bin - 119.080
pd14shim.bin - 119.080
pd14udsi.bin - 119.007
pi1400si.bin - 201.104