While there are pretty hi-tech cell designs available these days, to my knowledge the 'pods' were a literary device. And you'll notice that while most characters 'customise' their outfits, they all wear the same prison issue pants and shirts.

Writer and show creator Tom Fontana (who, by the way, is of Sicilian descent) set out to create a hyper-realistic show; that is, an exaggeration of the worst aspects of prison culture. He set out to include as many criminal subculture's prevelant in the North East of the US from the early 90's to early 2000's as possible, and created the concept of Emerald City to allow the interaction. This sort of thing is actually pretty rare in prisons (for example, officials would not intentionally throw members of rival gangs into the same divicion, or put Aryan's in with black dudes, etc)

Nothing for nothing, but if you search the archives, there's a couple threads on the show floating around.