Skype has announced plans to charge iPhone users for calls made over AT&T's 3G network later this year.
The company has also stated that it has no plans to introduce charges to Verizon Wireless' smartphone customers who use the same feature.
This follows Skype's success in bringing the 3G VoIP service to the iPhone. Since its launch on Sunday, the Skype 3G application for the iPhone has been downloaded five million times.
The previous Skype application only allowed users to make calls via Wi-Fi.
Speaking to the Los Angeles Times, Skype spokesperson Jennifer Caukin said: "We've thought long and hard about this for a while. It's the first time that we've monetized out mobile products in such a way."
When asked why Skype is charging iPhone users, but not users of Verizon Wireless smartphones, she said it Skype would be affordably priced and in line with the value it provides to iPhone users.
The move marks a U-turn by Skype, after a spokesperson last July said that Skype-to-Skype calls would be "always free, forever."