How do you use Pingo.com?

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I have noticed the existence of this international calls service on the web called pingo.com. I didn't register it, because I was afraid it might ask me credit card info. This website is about making calls from United States to anywhere in the world with cheap rate. But it also mentioned about "Soft Phone". I just want to know if I can make a call from my cell phone to somewhere like Mexico, is that possible. Or Do I have to use computer to make such calls, which make no difference from Magic Jack?