For what it's worth, I'm a 30-something now but when I was a middle-school and high-school kids, cell phones weren't really something most of us had. We still didn't bike much - I'm an outlier for familial reasons but my peers as well. We still found other things to do inside - video games for instance - but Instant Messaging was already starting to replace "face time" among my friend circles by the time we were 8th graders or so. Probably earlier now that I think of it. If anything, having a cell would potentially make us more willing to go out and do things, since I don't need to be glued to my computer to interact - can shoot texts around readily enough regardless of where I am.
I think I had maybe two friends in that era in bike-able range. The rest lived easily 13 or so miles off - physically possible but frankly I don't think I ever thought to even try and bike there. Would have taken ages anyways.