I have been using Viber the past few days to see if it will work. Voice calls only really work well on WiFi, even if the WiFi is connected only to a 1 megabit per second (Mbps). The hard thing is finding a VOIP app that works with 3G/HSDPA connections in places where the 3G connection is not all that fast.
Testing from Starbucks, Alabang Town Center, I was able to download a 10 Megabyte (MB) file from the Android Market in about three minutes. Since 10 MB's is 80 megabits, we should be able to download a 10 MB over a 1Mbps 1 minute and 20 seconds. Slowdowns could also be cause by the server where I downloaded the file. But I do have a decent 3G connection, well by Philippine standards anyway (except when I am in Makati, where my Smart 3G connection is sometimes even faster than the available WiFi connections).
I tried two calls from the same location on 3G, one from Skype and the other from Viber. The phone I was calling was a Apple iPhone 4 with Skype and Viber installed. The Skype call did not go through. The Viber call went through but got cut after 45 seconds or so, with Viber telling my the data connection was poor. So, better than Skype, but we have not yet found the grail. Still, not hard to see why it is the top trending app in the Android market these days.
Battery usage when on standby seems to be minimal, but it does not show up in Battery Use interface, so I am not sure. But I have not noticed any discrenable change in my battery life the past four days. Still it would be nice to have the option to turn it off, or to connect it to WiFi so it only goes on when on WiFi. They really need to pack larger batteries in our Droids so we stop obsessing about things like this.
The nice part is when you install it, it finds all the people in your address book who use Viber. With over 300 contacts, I only have 5 on Viber. Had a friend download it so we could test it, and he appeared in my contact list right away.
All in all, a very nice Android and iPhone App. I would not mind trading in some voice quality for light network requirements. Between network quality, and few users, it might not be appropriate for some developing countries. An off button would be welcome, so it can just be used for scheduled calls on WiFi. Still, messaging through Viber works fine, even voice calls are a no go, so that it is a fair reason to keep it on even when on 3G.