Following are useful parameters to be changed all in one go:

Enterprise Parameters:

Auto Registration Phone Protocol = SCCP << Very Important if this is SIP then all your phones will load SIP firmware

Connection Monitor Duration = 10  << Default is 120, by minimizing the time duration, you can speed up your the process of your phones falling back to Primary Call manager from SRST

Phone URL Parameters = Change the hostnames to IP addresses << If this is not done then many phone services will not be accessible.

Service Parameters:

T302 Timer = 5000  << Interdigit time-out
G722 Codec Enabled  = False

Stop Routing on Unallocated Number Flag = False
Max Forward UnRegistered Hops to DN = 2

Transfer On-hook Enabled = Enabled
Forward No Answer Timer = n

Default Inter-Presence Group Subscription = Allow Subscription
CUP PUBLISH Trunk = <SIP TRUNK for CUPS server>

Device Name of GK-controlled Trunk That Will Use Port 1720 = GK-Trunk
Intraregion Audio Codec Default = G729  << This is Important for Gatekeeper calls

Built-in Bridge = Enable

Message waiting Lamp Policy = Primary Line – Light and Prompt

Preferred G.729 Millisecond Packet Size = n ms

Allow TCP Keepalive for H323 = False
Allow peer to preserve call = True

Call Park Reversion Timer  = n

n= any value as per requirememt