VOIP is becoming a solid alternative for business telephony, especially businesses that have already invested in local and wide-area data networks. VOIP can be added onto an existing data network relatively simply, although hardware costs at start-up can cost thousands. And VOIP business plans, with unlimited domestic and low-cost international calling, can mean huge savings for a business. It's not as easy for a business to get cost numbers from providers, since most of these are custom solutions. But for businesses -- from small to large -- a VOIP Plan can be a solid investment.