While your phone is connect to a Wi-Fi network, placing calls over the Internet is better than over your mobile network. The LG Nexus 4 comes with the Android SIP VoIP client feature, so it is easy to use SIP-based Voice over IP services.
How to Set up a SIP VoIP account on LG Nexus 4 phone
* Launch the Phone app and touch the Menu icon.
* Select Settings >Use Internet calling. Touch Accounts, Add account and enter the details provided from your SIP provider or company IT department.
* When the details have been finished, tap the menu button and save it.