It is quite dangerous to give out your phone number to people you don't know. You will have to do that in many cases: online lists, new contacts, subscriptions etc. Fortunately, there exist services that give you an anonymous virtual phone number that you can give here and there without fearing being spammed or harassed later on. Your caller or callee will know only the virtual phone number while your phone will ring through your real line. Here is a list of the most popular of such services.
Spelled without the e, numbr.com is the new name for craigsnumber.com. It offers you a completely free anonymous number in a very easy way. Just log on to their site and register for a new number, which you can get only seconds after clicking. You can even have a new number if you are away from your computer, by making a simple call on your fixed or mobile phone. Each number is unique and is not recycled. There are also features like call-screening and anti-telemarketing. You can keep the number for a length of time ranging between an hour and a month. The strong points of this service are the ease of use and that it is free.
Jetnumbers service gives you virtual numbers in more than 50 countries around the world and in more than 3000 area codes. You can be anywhere and have a number with any area code, anywhere. People calling you from these area codes will then only pay local rates. There is also voicemail among other features, including SkypeIn for a much extended list of countries.
Vumber is a very good and easy to use service. You can choose any area code you want to get a number with that area code. Plus you have many other features. With Vumber, when the phone rings, you can decide to either take it, send it on mail, play a tone, put it on hold etc. The service is however not free. While I am writing this, the service is at a nominal price of around $5 per month.
Jangl allows you to call or text anyone while hiding your number. Again, getting the phone number is not straight-forward; you have to tell them who you want to contact and they will give you a number for that call. As I am writing this, Jangl is in beta and is free. Once they release, the service will be paid. Despite all these, Jangl is a strong service that has become very popular.
SaferCalls service offers virtual numbers and voicemail, and extends to international calls, but with additional rates.
Ring-To Number gives you a free anonymous number that you can use on social networks, but requires you to place a widget on your personal page that will generate the number. The service is free, but there is a premium price for those who want to get numbers with area codes.
oncetel offers free anonymous phone numbers, but people who call you on these numbers will have to pay small fees. What is also good with oncetel is that you can get the number instantly online through their web interface.
Call Safe is also free, but charges a small fee for the person calling you on the anonymous number. The duration of your number ranges between an hour and a week.
Stealth is a service with many features, but it costs a nominal monthly fee. Also, obtaining a number is not instantaneous.
Tossable Digits is a paid service giving you an anonymous number, with features like call screening, voicemail etc. Subscribers have a 30-day period and 1000 free minutes at the start.
MyAdBox is a privacy package that has plans ranging between $5 and $20, all offering an anonymous phone number and email address. You can even set up greetings. It is principally designed for people placing ads on newspapers, web pages or elsewhere.