There are LOTS of options, each with their own Pro's and Con's.
Which might work better for you Depends on your exact hardware, bandwidth & associated SLAs (jitter/latency, etc), budget, and more
The most reliable and straight forward? a landline connection to commentator, with local phone handset/setup then allows wired audio connection into OBS PC (Bluetooth might be easier but has its own whole raft of potential 'random' glitches mid-event). Wired beats wireless almost every time for performance and reliability. Depending on cellular network, a cell call (again, I'd recommend wired connection of audio from cell phone to streaming PC) might work [large stadium with large crowd and overloaded cell network... obviously more chance of problem than a youth event with a hundred audience members vs thousands)... lots of variables to consider
Anything that uses the Public Internet has potential jitter, latency, and throughput issues. There are ways around that, most of which cost $ (varies depending on how much bandwidth and reliability you want)