This is NOT a custom. It's official merchandise! I was lucky enough to find this and nab it! I've never EVER seen any merchandise for Freefonix aside from the CD album they released. This t-shirt was, according to my source, a prize in a competition. It's a child size tee (though it fits me as a small lady's tee) and it's a dark grey with the Freefonix logo on front and back in neon pink with stylised embellishments around it on the front design. It had no tags and I think only a handfull were ever made. It certainly wasn't ever produced for sale to the general market, to my knowlege anyway, or they would be everywhere.
Those who remember, I had a custom printed Mantyz tee a couple of years back that I did. Mantyz never got any merchandise at all, not even an album. Maybe because they were the bad guys or maybe for complicated musical copyright reasons since the guy who sang for them is very well known. I've no idea. Or maybe because the show was cancelled before anything like that could be produced.
Anyway, I'm so happy I found this! It's really exciting to find a rare gem from a fandom you adore. Also, appologies for the strange rainbow line down the photos. The light was poor and my iPhone's camera was struggling.