Ah more stupid fan service shit.
Duh. It's Japan, what do you expect? Unlike here in the west where we frown upon such blatant displays of sexual objectification of women, they have no problem with it over in Japan (well, except for maybe Tokyo, but that's an entirely different matter). It's a cultural thing. Besides, it's not like the phone cards are being sold here in the west, so you don't have to deal with it. You also forget who these cards are actually aimed at.
In regards to what phone cards are, I believe they are like prepaid cards that you use at public phone booths. You have different color booths that symbolize the primary function of that phone booth. Unfortunately, I don't know what the colors mean though, *derp*. I could be wrong though. Maybe they're for cell phones instead, lol. I use prepaid cards for my cell phone.