The Genesys Callback Push Notifications iOS Sample Code demonstrates how to send asynchronous messages (push notifications). While iOS uses APN (Apple Push Notifications) and Comet, Android employs GCM/C2DM and Comet.
A long time ago in Internet years, in a galaxy not so far away, a handful of tech titans in Silicon Valley and Seattle began building business platforms and battling for supremacy. The mobile device and app revolution hadn't yet begun. Terms like "social networking" and "wisdom of crowds" were going “viral". Web services and APIs were still emerging. The Google IPO of late 2004 had effectively slammed shut the Web 1.0 dotbomb era, paving the way for the amazing evolution of Web 2.0 services in 2005 that hit the mainstream in 2006.