It https://www.sip.us/advantages-of-sip-protocol/ is no exaggeration to convey that today you can't chance a business lacking an efficient phone system. Almost all business enterprises abjectly depend upon an office building telephone system in order to connect to their customers, field staff, distributors and other stake holders to conduct their day-to-day operations.
The answer is... few. In fact, once providers and manufacturers have certified their configurations, there is little if any noticeable difference to the marketplace. In fact, the main advantages of SIP give a significantly greater range of flexibility in terms of multiple location business while at the same time affording greater efficiencies with existing resources.
Since the federal government hasn't yet decided how to categorize services like VoIP (though, VoIP experts agree that may happen at some time), that means that it isn't really put through the same form of regulatory guidelines (and scrutiny) as conventional telecommunications services. That impacts their cost of doing business- VoIP agencies can operate more cheaply than the usual regular telephone or cellphone company, which enable it to offer features that other telecommunications services might be lacking.
As for routers, I like the Cisco WRVS4400N gigabit router. Trust me, the wireless router supplied by your internet provider may work, but it is not high enough quality for small company needs. Good cabling will likely be had to ensure you get the most effective transmission over your network. Category 6 is the thing that I recommend. I am always amazed when business owner/IT manager can't answer questions about the type of cabling he/she is employing or who installed it. You can have the top IT equipment, if the cabling is poor, it will likely be all for not.
As far as other aspects of VoIP infrastructure go, you probably curently have an Internet connection that's geared towards high-traffic. Nonetheless, it is vital that you talk to your ITSP plus your IT administrator as to how we are going to provision the mandatory bandwidth for smooth Internet voice communications. The best practice is to create a Virtual Private Network or even a VPN that can have always the mandatory bandwidth available for simultaneous VoIP connections. As your organization grows and as the number of employees increases, this limit must be constantly raised maintain.