Three services stand out. All offer just about every conceivable feature a phone service can provide, all included in the low fee as compared to traditional phone service.
ViaTalk offers the best deals on VoIP phone service. Their special incentives are always changing, but have included a free second year of service when you pay for a full year in advance and a free second line.
Packet8 offers pricing almost as low as ViaTalk, but where they stand out are their Business Plans. If you are a small business owner who wants to appear like a larger company, you should check out Packet8's Virtual Office with iPBX.
Packet 8 also offers some very atractive international rates.
Vonage is the largest, non-cable company, VoIP provider out there. They are a little more expensive than the two above, but provide extremely reliable and clear sounding calls. Despite recent patent law suits that have been settled, the size of the company virtually guarantees that they will be around for a long time. This can be a concern, as smaller VoIP companies have gone out of business.
Time Warner offers Digital phone service, but to get unlimited national calling, you must pay at least $39.95 a month. That's up to $20 more per month than the other services and doesn't even include voice mail.