Sorry everyone - there's no such thing as a Red Box for cellular phones. Sure, with the right equipment, you can clone an analog (AMPS) phone and steal access to somebody else's account. But that's been common knowledge since the 1980s, and it doesn't work with modern (TDMA, iDEN, GSM, CDMA) networks anyway.
If your idea of phreaking is to find out moderately interesting things or various technical details about how mobile phone companies operate their networks, then sure, there is plenty of information available that you can find out either from observing your phone (in its various debug modes) or by looking on the Internet.
However, if by phreaking you mean "obtaining free cellular phone or data services for which you would normally have to pay" or "finding out how to listen in on someone's (non-analog) cell phone calls," then you are not likely to succeed, as there are no known practical methods for doing this. Well, actually you could commit identity theft or just steal some money and use it to pay for your cellular service, but I think that that falls a bit outside the realm of phreaking.
Why bother making a webpage about this? Well, if you search for "cellular phreaking" or some similar thing, you will find tons and tons of pages claiming to have information about this, but mostly they just want to make you look at their advertisements while sending you free ringtones and trying to get you to vote for them on some "top 100 sites list" or some such thing. I find these pages irritating and I am hoping that this page might help set the record straight.