Sipdroid
![screenshot](https://rootpk.s3.gra.io.cloud.ovh.net/screenshots/6455caff933c877d38191089-1.png)
![screenshot](https://rootpk.s3.gra.io.cloud.ovh.net/screenshots/6455caff933c877d38191089-2.png)
The app routes calls dialed from your phone's built-in contacts app to VoIP. In settings you can choose when to use VoIP and when to make standard phone calls, based on being logged in to Wifi, and/or based on number prefixes. Visit sipdroid.org for more info. For optimal battery usage reserve a free VoIP PBX on pbxes.org, and manage your SIP trunks using a web browser. Being open source, Sipdroid has often been cloned appearing under names such as Guava, aSIP, Fritz!App, ...