I think you're overthinking things on the phones. The trolls can already circumvent blocks and bans, they can just hijack a phone call...if it even IS a phone call. If it's like a group voicechat, they'll just keep kicking Karkat and he'll keep coming back.

"Mobile phone group chat server apps with voicechannels weren't really a thing in 2009" we don't know if this version IS set in 2009