With the Push support in the iPhone OS 3, the iPhone has become an excellent platform for instant messaging.
Before the Push support, you could only keep them listening using hacks like Backgrounder on jailbroken devices or using clients that forced the entire phone remain “alive”. Neither is an optimal solution. Now, the Push support provides the platform with something that, in some respects, is even better than the current instant messaging support on competing smartphone operating systems (at least Symbian S60, Blackberry and Windows Mobile).