Config Sample on the VG side. This sample includes the config for only one analog port on extension 3334445555 but it would be the same for all other ports.

interface FastEthernet0/0
 ip address 10.10.10.10 255.255.0.0
 duplex auto
 speed auto

voice-port 2/0
 disc_pi_off
 input gain 10
 output attenuation 10
 playout-delay minimum low
 cptone HK
 timing digit 53
 description cflow1
 music-threshold -50
 bearer-cap Speech
 station-id name ashwin
 station-id number 3334445555
 caller-id enable
 ren 3
 disconnect-ack
 loss-plan plan4
 idle-voltage high

dial-peer voice 1 pots
 service stcapp 3334445555
 port 2/0

dial-peer voice 10 voip
 destination-pattern T
 session target ipv4:10.10.20.50 (CUCM IP Address)
 session protocol sipv2
 codec g711ulaw

dial-peer voice 10 voip
 incoming called-number .
 session protocol sipv2
 codec g711ulaw


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Sample config the CUCM Side 

Route Pattern
Pattern = 333444XXXX VG_PT
Route List/Gateway = VG_RL (VG RG > VG SIP Trunk) 

Make sure the route pattern is in a partion that the intended phones on the CUCM side can dial.