http://www.techcrunch.com/2009/07/05/ch ... fi-or-not/
Here’s how it works: Cherry - which is essentially an MVNO - pre-installs software (so yes, in the demo there was actually an application running in the background) on smartphones which it will sell as a packaged product, starting with a Symbian version for Nokia E-Series phones and expanding to other platforms later. Once activated, Cherry lets you call your contacts either over Wi-Fi or the GSM network when you insert a SIM card. Take out the card, and you can only call over a wireless Internet connection.
