Beta 4 has been more stable, but I am seeing constant baseband crashes.
I am seening this behavior on two iPhone 6s Plus'.
Cellular/LTE will drop for 10-20 seconds and it will recover.
I know most of us are using wifi connections with development units, but if you see this behavior please submit a bug report through the Feedback app.
The issue has mostly popped up when web browsing in Safari, so it might be related to webkit, but I am not sure.
Downgrading back to iOS 10 beta 3 has resolved the issue for me.
Anyone else?