the short answer is NO, but the longer one depends a lot on you. Voice mail systems are pretty much standard all around, but few people realize what a security risk they can pose. On the surface, a phone seems pretty harmless. What are they going to do? Leave me a threatening message? Well, maybe, but that's not the danger.
Most people choose to leave a custom voice message on their voice mailbox. Something like "Hi, you've reached James Voca, IT manager for Pirulo systems. Please leave your message and I'll call you back" seems pretty ordinary, doesn't it? Well, for an employee giving you a call, it is, but if someone outside calls in, you just informed him or her which company it is, what's the name of the IT Manager, and how he sounds like. In the wrong hands, this data is very valuable. A type of hacking known as "Social Engineering" focuses on using peoples tendency to behave socially can use exactly that. A social engineering hacker would typically call employees of the company on the phone, and try to get them to give out sensitive data or access. With the info from this mailbox, the hacker can pretend to be the IT Manager, and influence others. Many users will recognize the high ranking position holder and tell/do anything he wants. They would give him their passwords, let him take over their computer remotely and more. Here's a scenario:
Hacker: Hi Jane. This is James from IT. I'm at home and late for meeting - do you mind if I log into your machine to get a PPT I really need?
Jane: Sure, James
Hacker: Cool. I'm sending you an Email with a link - just click it and I'll be in and out in a minute.
Outcome: Hacker can implant a backdoor on Jane's computer, or just use it to get access to some sensitive internal servers.
How about another scenario:
Hacker: Hi Scott. This is James from IT. A guy from HB is coming in to pick up my laptop for repair - be sure to let him through, OK?
Scott (security guard): Sure thing, James.
Outcome: The hacker can waltz in the building, grab some laptop and disappear with it, causing both financial damage and possibly stealing important data from the computer.
This is not the only danger, of course. Most modern voice mail systems let people access them remotely. You would typically call yourself, punch in some PIN and can listen to your messages. Many people don't want to remember complicated numbers, and set the PIN at 0000, 1234 or the default (which is often one of these too). When this happens, anyone else can call into the voice mail, guess that number and listen to your messages. These would usually be just some nagging from your Bank, but they could also contain sensitive info. For example, it could be a message from your doctor about your blood work, a message from a vendor talking about things you purchased or worse. A hacker that knows how you sound like, and that you've just ordered 10 servers from Deck.com can call them, quote back some "secret" info from the message, and divert the goods to his house. He can also call you, pretend to be the vendor and get you to let him in the building with the "servers", and a good opportunity to do some damage.
The lesson here is simple - don't think that the voicemail system is safe, just because it's not connected to your computer. In fact, your own answering machine at home could expose you personally to some dangerous elements. Does your message sound like "Hi, you've reached the Smith family at 2245 lake drive"? You're just inviting people to come over and clean up your house. I recommend taking four measures:
1) Have your PIN secure - no simple numbers, but ones that are chosen carefully, changed frequently and aren't easy to guess
2) Have your message give as little info as possible. A good one could be "Hi, you've reached Jack - please leave a message". Same thing at home - "You've reached the Cole residents, please leave a message".
3) Listen to your messages frequently, and delete them. right away. Don't leave messages to linger on your phone from Friday afternoon to Sunday noon.
4) When you are leaving messages to others, whether you are a vendor, a client, a boss or a subordinate, keep in mind that you can never know the level of security the other side keeps. Treat a message left like a note left on the door - others may read it. Keep sensitive info out of the message, and just call back later.