There are a number of cheap services that you may want to look at. However, for your needs I would actually recommend a PBX system. They still use VoIP as the way you call in and out etc. but a PBX also gives you a call in system with queues, hold music, multiple extentions etc. Take a look at http://www.voiprater.com/pbx.php for a few of the top recommended PBX systems.

You can also visit the voip review page there as well if you just want to get a cheap VoIP phone line. Most VoIP services can be had for under $20/month with unlimited in and outbound calling. For a PBX, you may want to do RingCentral or Nextiva. Nextiva is only $8.95/month for the cheapest plan. Take a look at the information on the VoipRater.com website and you should be able to research and find which company will best meet your needs.