Another prepaid MVNO has entered the market. cool.Prepaid is using Cingular's network and is offering Motorola's RAZR V3 to subscribers who want a new or upgraded phone. cool.Prepaid will offer service costing 30 cents a day and 10 cents per minute for calls in the U.S. The MVNO is trying to differentiate itself by offering cheap international calling and is also working with Motorola to deliver iRadio services to its prepaid subscribers. Subscribers can call several countries for an additional 10 cents per minute. It's unclear who the backers of this MVNO are. The company says it's working on offering data services later. With the plethora of prepaid MVNOs coming into the market, it's getting more difficult for these companies to differentiate their offerings.