What are some alternatives?
When comparing Eir SIP Voice and VoIP.ms, you can also consider the following products
Phonebooth - Phonebooth is one of the leading voip providers, providing phone systems & phone service for small businesses.
Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
Mitel - Business Communications and Collaboration
Loop Communications - Loop Communications provides hosted VoIP business phone systems to small businesses and mid-sized companies.
VoipSwitch - VoipSwitch provides complete VoIP and unified communications solutions.
XO Hosted PBX - Hosted PBX is a scalable UC solution that uses cloud technology to integrate HD voice & data services, mobility, along with advanced calling