If you buy the current 4.0 license you are able to download and run any previous version, I think back to 2.0... including 3.8.6... fyi 3.8.7 should be out shortly. You will never need to pay to upgrade until the 5.0 series comes out and then only if you want to upgrade.
As for the phone I never tried- you buy it from
www.vbulletin.com - don't know if they have a phone number posted or not.