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If you enable the Click to Dial/Fax option in your RingCentral desktop application, you can use the following VBA code assigned to a Command Button to initiate the call programmatically.

Note: Change "Me.txtPhone" to the relevant field on your MS Access form.
Alternately, you can use the DLookUp function to refer to a table.

If IsNull(Me.txtPhone) Then
DoCmd.CancelEvent
Else
Application.FollowHyperlink ("callto:" & Me.txtPhone)
End If

I also don't have experience with VBA, but here is some regular VBScript I wrote a while back to send a fax with the RingCentral REST API which might help.

https://github.com/grokify/ringcentral-sdk-vbs/blob/master/demo/demo_fax.vbs

I have no experience doing VBA development. RingCentral provides industry-standard Restful API. So as long as your code can invoke Restful API, it is possible. Please post detailed questions when you have them.