The error message stated you have configured an SRST provider, but the device does not appear to be responding as an SRST server. If you are relying on SRST and see this warning, the VG248 might have difficulty using SRST services if connectivity to Cisco CallManager is lost.
Check the configuration and status of the SRST device.
The Survivable Remote Site Telephony (SRST) feature provides the Cisco CallManager with fallback support for the VG248. SRST enables a router or other nominated device to provide call handling support for the Cisco IP phones when the Cisco IP phones lose connection to the Cisco CallManager. Survivable Remote Site Telephony (SRST) indicates that there is an SRST device capable of providing Cisco CallManager functionality with a limited feature set. If all other Cisco CallManager servers are unreachable, this device assumes control of call processing.
For further information click this link.
http://www.cisco.com/en/US/docs/voice_ip_comm/vg248/1_2_1/english/configuration/guide/vg248swv.html#wp1029275