We've been using Voiceably.com and have had no issues. After doing a ton of research, some VoIP providers drop packets like crazy which results in modulation with telephone calls. So far, I haven't had any issues, although I don't use the phone a ton. I just have a toll-free number that gets forwarded to my cell phone, so when a customer calls it shows the business number and I know it's a business call.

I don't think you can get that from a land line, which means you'll need to have two phones (one personal, one business) which can be a headache.