For those still using analogue or digital phone systems, voice on ISDN circuits has a bandwidth of around 4000Hz. The audio from an analogue phone is sampled at 8000Hz, and because of the nyquist theorem, must be low-pass filtered to 4000Hz. So any frequencies in the audio beyond 4000Hz are lost. Interestingly, the human ear and mind are good at recognising human speech, so this is considered "toll-quality" voice, i.e. good enough to pay for. This is the reason why certain vocalised letters are difficult or impossible to tell apart on the phone. For example, the differences between B, P, T, C, etc. are almost entirely above 4000Hz.
The biggest advantages are that it’s free and you have the ultimate flexibility in what you can say. If you plan on using background music make sure you’re using music that is safe to use in commercial projects. Also check out the technical requirements of you business phone system and learn how to format on hold music for phone systems.

It's a panoptic experience, being on hold while listening to someone singing about being on hold. Depending how long it takes for someone else to join the call, you could be listening for awhile. The music builds as time goes on, culminating in a spoken verse that begins: "Well, let me tell you all a story / about a man who was on hold all day..." This unusually self-aware song is the default music for a conference call service called UberConference, where "I'm On Hold" plays on a loop for anyone who calls in early, on almost every call that doesn't start exactly when it's scheduled to (or doesn't ever start at all). It's selected by nine out of ten call organizers, and plays over a million times per month, says Craig Walker, CEO of Dialpad, owner of UberConference.
Do you need benefits and eligibility information faxed or emailed? Just call this number to access our automated Voice Portal. Dental offices can receive patient information via fax or email. Members may receive eligibility, benefits, and claims information via email, as well as lists of participating dentists in their area. Please make sure we have your current fax and email information before submitting your request. To verify, visit our website at w w w dot delta dental n j dot com. Log in to Benefits Connection. Click “Profile” under “Other Tools.”