I envision a scenario in which Skype provides totally free outbound calling to those users who sign on for the revenue-generating SkypeIn service. Free world calling could, then be an incentive that would drive registration for Skype’s paid services.
This will, I believe, be instituted with a monthly free-calling maximum allotment of minutes. 500 minutes a month would be about right. This would act as a brake against wildly enthusiastic use. The maximum minutes control would also be fungible, and be subject to adjustments that could be made for promotional purposes.
New users who sign up for free Skype anywhere in the “whole world” would, then, only be eligible for this if they buy a SkypeIn number. Makes sense- that way all their non-Skype-using friends they start calling will want a number to call them back.
Read this item from ZDNet’s IP Telephony, VoIP and Broadband Blog