In addition, please read the Guidelines for Quality posts. Inquiries and questions don't earn you quality post credits. You need to make some discussion in your own words that is more than one sentence long.
I don't see a sense in having Voip PBX on VPS. Without backup and VPS down, you have to re-apply everything from scratch, eveytime VPS is signed-on ! It's generally not intended for permanent job anyway, VPS I mean.