Yappd was developed, like most applications, to fulfill a need. We wanted something that not only allows you to know what your friends are doing, but also allow you to see what they're doing as well. Yappd does just that, it allows you and your friends to keep each other in the loop. You can accomplish that by posting a yapp through the website, by sending an e-mail, text message, or picture message.
It seems to me now become too many clones of Twitter. I've also checked the features of this Yappd, it only allows USA phone carriers. I think Jaiku already did way much better and reliable stuff than that. I can't see a potential of this application as you can see techcrunch also thinking likewise.