At this time, the limit is 4 hours and is by design. We do not currently have any plans to extend this time frame as its main reason for implementation was to reduce network congestion in the event of unnecessary/accidental calls not being released from the network.
If you and your friends have unlimited data plans or are in a location with Wi-Fi, you might benefit from some other 3rd party VOIP calling services like Google Hangouts, Skype, Facebook messenger. My friends and I use Discord which has an always open voice channel and users can stay connected to it as long as they want. It's as a downloadable PC/MAC app, browser based, or as a mobile app that can be downloaded on Android and iOS. You can also have text only channels if you want to keep the convo going after folks have left the voice channel.
The thing is, we hate using anything else because everything else something
always goes wrong. Skype uses too much space and doesnt work half of the
time, Messenger is very buggy and we can't hear each other half of the
time, ect. We dont want to install an app just to call when we do the exact
same thing with our numbers. Me and my partner like to record our calls for
memories, and it only records calls. If there will ever be an option for
extending calls, that would be appreciated. I dont understand how anyone
can not notice an accidental call when tbe duration is 4 hours. If that's
the case, simply Im put an option that when it's 3 hours and 30 minutes
into the call, an option pops up saying "Hello, would you like to extend
this call?" With a yes or no option. If chosen yes, the call at 4 hours
will continue, but you will get another notification after another 3 hours
and 30 minutes, ect.
If chosen no, or left unanswered, the call will end at 4 hours.
It's bull when the people who pay for unlimited have to use another app for
the same purpose you pay for in the first place. I rather just switch phone
plans if that's the case and go somewhere where they will actually give me
the options i want for what i pay for.