Trying to set up a VPN server on an Arch Linux box. All I want is for it to be usable by OS X and iPhone OS. I'm a noob at VPN and can't seem to have much luck Googling. What software do I need to install and what else do I need to configure?
Recommended reading: OpenVPN Howtos
OpenVPN works fine on OSX. To work with iPhoneOS, though, you're going to need a L2TP, PPTP, or IPsec server. Free/OpenSWAN is pretty easy to set up these days if you.
Honestly, the OpenSWAN documentation is pretty good, but you can find Gentoo instructions that are reasonably applicable to Arch (the default kernel config should have the options you need, so you can skip that part) here. Relevant OpenSWAN docs are here if you want to do L2TP (which makes interop with Windows clients a lot easier).
As nice as certificates are, the easiest solution is getting a PPTP server setup: https://wiki.archlinux.org/index.php/PPTP_Server
If you want to use OpenVPN which is one of the best in terms of encryption and speed, you can't really use the native methods of iOs (L2TP, PPTP or IPSec).
There are three major families of VPN implementations in wide usage today: SSL, IPSec, and PPTP. OpenVPN is an SSL VPN and as such is not compatible with IPSec, L2TP, or PPTP.
But there is now an iOs app that allow you to link a profile and easily connect to an OpenVPN server.
You can read the ArchWiki to install OpenVPN on your server here.