"What's your opinion on online BDSM play?'
It's completely voluntary and self-discretionary, so what's not to like? How anonymous you are is up to you. What you reveal about your kinks and yourself is up to you. Which people you befriend is up to you. Generally, everything is up to you. You just always have to keep in mind that once you put something out there about yourself, it's out there forever, so you have to be careful.
If by BDSM play you mean, like, acting out a virtual scene or something, then I don't really get that. But I never really "got" phone sex, either, and clearly there are LOTS of people who enjoy that. I think phone sex sounds ridiculous.