Hey Viber, once more:
Why does the Viber app on my iphone request http://www.cdn.viber.com/ok.txt every couple of minutes, even if the app has not been running for weeks and is not right now?
These requests keep coming even when Viber is killed or was never started since reboot. This is not inline with Apple's Guidelines.
Furthermore, you do not need such a GET hearbeat to function. Your "calls" use Apple's Push Notification Service to alert the user, which is smart and right. APN can be delivered without such a heartbeat and that what APNS was invented for.
Last but not least: Your GET requests request a "keep-alive" in the header, which might cause avoidable battery drain. I haven't verified this yet though. Nevertheless, I still don't see a rational reason for this ominous heartbeat signal. Both its origin (crontab?) and its intention (redundant due to APNS) look suspicious and questionable -- and, most important, avoidable.