You can find a SIP provider (Flowroute, SIP.US, SIPSTATION.com, Twilio, OnSIP, and many more) that will allow you to either use a desk phone or a software-based

You can find a SIP provider (Flowroute, SIP.US, SIPSTATION.com, Twilio, OnSIP, and many more) that will allow you to either use a desk phone or a software-based phone with a telephone number of your choosing. It's never free, and you can expect to pay $0.009 - $0.02 per-minute for all calls. Disclaimer: I work for one of the companies that I listed in parentheses.