It seems no one was really prepared for the huge demand for the HTC Evo 4G. Not only did Sprint and other retailers run out of the devices, but Qik, the provider for the Evo 4G's video chat app, was also overwhelmed by the phone's popularity and ended up having to temporarily pull the app.
Actually, the problems started early for Qik when customers complained that they couldn't even find the Qik video chat app in the Android Market, but fortunately, Google quickly came up with a workaround so users could discover and download the app from the marketplace. However, once that happened, Qik was deluged with users and its servers were hit with 20 times the normal workload.
As a result, users were met with frustrating connectivity issues, and subsequently, Qik decided to pull the app until it can make provisions to add more capacity. There's no word when it will be back, though you can check out the Qik blog for updates or to express your frustration. Also, remember, the Evo 4G isn't tied down to Qik; you can use other apps like Fring to make video calls on the smartphone.