go on ebay and buy a phone system. try a partner acs release 6. you can buy one 18d phone, and use analog phones for the rest. play with it, and start from there. install it for your home on your home phone line. avaya.com has manuals for free. after that, buy a small [16 mailbox] pcmcia type voicemail card off ebay, and set it up, then play with it. after that, sell that small pcmcia voicemail card, and buy the large pcmcia voicemail card, and play with that.
should be able to get this equipment for less than 500, and sell it when you are done for the same. if you can figure it out from the manuals, you can do what i and most 'phone dudes' did, and should be able to find a job, then move forward with bigger systems. that is what you would do if you started working for someone is figure it out for yourself with a manual in most cases, as even if they have someone show you how to do the job. he probably will not help you learn it much, other than have you work with the wires.
if you are not ready to learn it from the book, and play with it until you figure it out, try a different industry.