what is the difference between a calling plan and an additional phone number"

[roofboard]

I have not been able to find any clear explination of the difference between 
1. Adding a "Calling Plan" 
and 
2. Adding a "Additional Phone Number"

Questions... Can zoom user have two different calling plans?
What can a "Calling Plan" do that an "Additional Phone Number" Cannot?
What can a "Additional Phone Number" do that an "Calling Plan" Cannot?

I have a cell phone which I would like to cancel, do I need to transfer it over as an additional phone number?
Does the additional phone number work like an alias for a calling plan? 

So many questions.... Please Advise! 

[Eliot]

calling plan permits a user to make outside calls.  without a calling plan, a user can only make inside, extension to extension calls.

additional phone number only provides a local telephone number to reach you.  this telephone number can be assigned to your ivr, call queue or extension.   

you can port your cell phone number to zoom phone.  you will be able to be reached at both your zoom phone number as well as your old cell number.  your old cell phone number will be connected to zoom.  without a mobile carrier, i do not think your cell phone will work.

a zoom user can be assigned more than one calling plan.

please see support article

Managing phone users – Zoom Support

[Eliot]

also, calling plan usually includes one local telehone number.