After some extensive searching with no satisfaction, perhaps someone here will have a solution. I've been using Skype to exchange messages between a Windows computer and my Mac computers and iPhones. I like the fact that I can receive messages on my Mac and/or my iPhone, so I don't miss communication. Many of these come from a Windows user. However, Skype is a resource hog on both my Mac and iPhone, which leads to more rapid battery consumption. I don't use the calling or video calling features, and only have interest in text messaging with occasional file transfers. Having a push feature on the iPhone would be useful, so I don't have to leave an app running all the time. I currently run Snow Leopard on my Macs, and with a Windows user involved, iMessage isn't an option. Also, I don't want to subscribe to my cellular carrier's messaging plan, since there are only a few that I choose to receive messages from. Has anyone found a simple solution for exchanging text messages that is lightweight, runs on all 3 platforms, and doesn't involve opening my phone to messages from people other than the few I select? Or am I stuck with Skype for now?