Kacey hated Alec. She wanted her saga to be the last and final one, and when Alec came along, it took the attention away from her (she was a total attention whore and I say this as someone who was friends with her through the very end). They might have done some calls together with Chris, but they never met in real life or anything like that.
Jackie's letters were written by Alec (it's very obvious if you read them and then read Alec's). I don't know who did her voice on the phone, but Chris's dating profile on some local site was found, and a bunch of us PVCCers made profiles and Chris happened to select that one to message (we couldn't message first or he would suspect it was a troll). I don't know who did Lars's voice, but I would imagine it was someone who knew the person who did Jackie's voice on the call.