Is there anything cheaper than MagicJack VOIP?

I have a server running all the time, so having a computer on all the time is not a problem. But is there anything cheaper than MagicJack where I can send/receive calls from people’s cell phones? This would require any phone number. Thanks!

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I am looking form North America to Poland (Cell to Poland is much more than land line). Again VOIP, and NOT Vonage, their service is absolutly a nightmare! I will be using cell that has VOIP technology