@rplatham, I see that at the bottom of page 1 of options for MCPE on iOS, but Windows 10 has broadcast to Xbox live and use cellular data at that spot. At the top of the page, where the iOS version has change name, Windows 10 has change gamertag and manage Xbox options. Both of which require internet connectivity to access. When online, manage Xbox options will let me sign out, but MCPE displays a sign in dialog stating please sign in with your Xbox live account to play with friends, earn gamerscore and achievements. Since there's only one button that says sign in and no cancel, I'm kind of stuck. Thanks for putting forth the effort and thinking about it. Very prompt, but it won't work for me.
I have the same issue. I took an old wireless router to my mother-in-laws to play with my son, iOS vs Windows 10. She doesn't have internet, but now v0.15.1 on windows 10 pops a message when opening world, "you must be connected by WiFi to play with your friends".
Stephen, we played tonight using my iPhone 6 as a mobile hotspot. It worked with no problems.