I still don't really understand the benefit of this over the native SMS app. On iPhones (and I imagine, other smartphones) reply all is available. And you can send pictures in the conversation. I'm pretty sure you can send map locations too, but I've never done it.
If there is no functional benefit to the app, it doesn't look nearly as nice, and my friends aren't hassling me to download it, why would I?
It replies via SMS or MMS to every phone number in the conversation, regardless of whether it is an iPhone or not. I can see your point about not having this capability on other smartphones, but why not build an android/bb app that does exactly that instead? (if it doesn't already exist)
If there is no functional benefit to the app, it doesn't look nearly as nice, and my friends aren't hassling me to download it, why would I?