At the end of each episode of Ro-Kyu-Bu!, and sometimes during the episode content, the girls are seen talking to each other or to the audience in chibi form. Usually there is 8-bit music in the background, and the characters appear to be sprites (without animations).
Is this a game they're playing? Or, is it something more meta (like a representation of them talking by phone)? If it's a game, does it have a name?
In the first episode of Ro-Kyu-Bu! SS, the girls are again shown in their chibi forms. It is then revealed that they are simply typing into their phones and computers as their conversation goes on.
Since they're doing this on flip phones, it seems unlikely that they're playing a game, despite the occasional "Now Loading" screen. The most likely conclusion is that the chibis are just a representation of each character chatting with the others, probably shown because it's more appealing than showing each girl on their personal computers.