Check out Google Voice for a simple free number that goes to voicemail. It s perfect for what you want.However if you re looking for a more professional solution for your business, I d recommend looking into a virtual pbx. These services offer more business-class features like an automated attendant and multiple extensions to send callers to make your business appear more established and credible to potential customers. Still very inexpensive ($10-$20 mo.), but way more professional and reliable.
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Google voice, maybe?Just tell them that you don t want their services, and you re logging each call if if you get more than three after you told them that you don t want to hear from them you ll hire an attorney and sue them for harassment and loss of business due to tying up your phone line and running up your phone bill.