Being in the same group isn't the issue...that has more to do with outgoing than how the calls ring. You need to makes the line ring to the same extension or vm group as the rest of the lines for company c. Check ring assignment in flash 40 programming.

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"Old phone guys never die, they just get locked in some closet with an old phone system and forgotten about"

Retired, taking photographs and hoping to fly one of my many kites.