phone to phone...unlimited SMS?
<p>I have an idea for an app that requires a lot of data exchange between users of the app. SMS seems like a very simple way to get this done, but is it safe to assume that all smart phone users have unlimited SMS? Otherwise this app won't be very popular due to expensive rates for SMS.</p>

<p>If this is really a bad assumption, can someone tell me what other means I should consider to accomplish this phone to phone communication? Initially I had hoped for an alternative that used data service instead of SMS. But I have read many (so many) forum posts about this sort of thing and have read nothing conclusive. </p>

<p>A bit about my app's requirements:</p>

<ul>
<li>Users build up a network of 'friends' for coordinating among them.</li>
<li>When one user creates some event on their device, all users in their network should be notified. </li>
<li>User's can also instant message other users on their network</li>
</ul>

<p>So, I need a mechanism for getting all of this done. After reading a bunch of tutorials, I can see how I would do this using SMS, just not sure if that's a good idea. Some people have said that this sort of job would require a central server, but I'm not quite sure how exactly that would work. I am not opposed to a solution that involves a server, I just need some help to get me started in the right direction. </p>

<p>Thanks in advance. </p>
