Ive been saving my grandmothers voicemails for almost 8 years now and when i went to upgrade my phone, i almost fainted when the rep told me they were going to be erased. Thanksfully he put us in touch with a company called http://www.voicemailsforever.com and they ended up much cheaper than the one you suggested above. i think your readers would benefit because they do it for so much less.
The telephone systems have the feature named as Voicemail. VoIP is the best example of it. When a receiver is unable to pick up the phone, then the caller can leave the voice message on the receiver’s phone. In older telephonic machines, such messages were stored as a voice message directly, and the receiver can hear them later. In modern telephone systems, such info is being stored on the server of the service provider in the user’s mailbox. It is similar to email in which the messages are saved in the form of audio instead of text.

Now select “Greeting” in the upper left of the screen. Tap “Custom” and then “Record” to record your personalized voicemail greeting.
Voicemail is a method of storing voice messages electronically for later retrieval by intended recipients. Callers leave short messages that are stored on digital media (or, in some older systems, on analog recording tape). Originally, voicemail was developed for telephony as a means to prevent missed calls, and also to facilitate call screening.