This guide will show you how-to check your voice-mail from any phone for free! This works well especially if you have some sort of unlimited long-distance phone system, like MagicJack, Voip, or Google Voice with a Friends & Family cellular phone.
There are two ways to do this. The first and easiest way is by calling your own phone number, then when your phone goes to the 'leave a voicemail' prompt, press the Star Key (called Asterisk in the phone world) and enter your voice-mail pin code and Bam! You're in.
There's a more complicated way to do this (and also a way to leave someone a voice mail without even ringing their phone or using Slydial [Slydial does leave your number but only rings for half a second]), but I'll add it to this post later because it's not possible to explain in a few words.