hi @sagy
Create a Desk Phone Provision Tempate for auto off hook dialing and bind the template to your waiting room desk phone.
this is an example of a template for hp/poly desk phones to auto dial extension 6766. You can change the extension number to whatever you need, but remember to enclose the extension number in double quotes in front of and in back of the extension number, i.e. "6766". Different desk phone manufacturers have similar but different formats for templates.

this is an example of the AutoOff Hook template assigned to a HP/Poly VVX 450.

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thanks, eliot