What can I do so that the calls don't have an 8-hour limit?

[nala5]

What can I do so that the calls don't have an 8-hour limit? 

[meself]

Not sure there us anything to change that

[MrGhoul]

Enable Wi-Fi Calling: Wi-Fi calling often circumvents the time limit imposed by carriers.
At&t is one of the carriers that doesn't have a cut-off limit.

[yamialex]

Just out of curiosity why do you need to be on the phone for 8 hours or more that one time