Just wondering if anyone could recommend a smartphone friendly app that my friends can use so we can all chat together while playing?

After the PS4 beta a few friends have decided to pick this up so now we are looking at options so we can all chat together. We all have either a PS3 or PS4 but Sony's party chat does not work cross platform but we all have iPhones so would something like Skype be the best bet?

We started playing DC Online last night just for a laugh while we wait for my friends PS3 copies to arrive and we were shocked to see the game itself has a built in cross platform voice chat system so we were able to talk even though some were on PS3 and some on PS4. I know Yoshi P. Has already stated that they will never implement such a system in FFXIV but I really wish they would as it made playing together so much easier on DC last night and during the entire PS4 beta you could tell that communication between players was a problem. There were no end of times I couldn't be bothered to reply to someone or I let parties fall apart because it would take to long to explain/type mechanics like Ifrits nail to new players using the onscreen keyboard.