Decades ago, in its heyday, Centrex earned its popularity by providing the functionality of large phone switches without forcing companies to buy the switches--big, expensive beasts designed to service cities, not businesses. The dawn of the PBX, however, saw the decline of Centrex as most companies brought their phone systems on premises. Although a PBX is nothing more than a scaled-down Class 5 phone switch--meaning some hardware woes remained--it seemed Centrex was forever relegated to serving government and education offices.
But the advent of packetized voice has increased the features offered by Centrex services, at a cost many companies will find hard to ignore.
IP Centrex provides all the functionality of a PBX, but because the service is provided by carriers, there's usually no additional equipment needed at the enterprise. Phone calls are brought in as data and routed over the internal data network to the appropriate IP phone. Of course the quality depends on how well your network can handle the extra traffic; see "A VoIP Wake-Up Call", for tips on determining whether your enterprise network is up to snuff.
But if you also want to access voicemail, place calls from your browser and gain easy Web conferencing and instant messaging capabilities, look no further than an IP Centrex service. For a small-to-midsize business torn between maintaining a PBX and outsourcing, the cost will likely be on par, but IP Centrex will offer you more features (for more on how to choose, see "The Business Case"; and for an overview of a company with a mix of Centrex and PBXs, see "Fidelity Matches Phone Service To Employees' Needs").
To determine just how far IP Centrex has come and what features providers are offering, we asked GoBeam, ICG Communications, MCI and Verizon to participate in our tests. Only Verizon declined our invitation, citing "huge" internal costs to support the test.
We asked the providers to supply us with a phone and access to their switches so we could look at features and functionality. Each participant sent us a Cisco IP phone, though the providers support a wide range of phones, including those from Polycom and Pingtel.
Our worst-case test network used an unmanaged ADSL connection. We set up a single public IP address at the router, while the rest of the network was privately addressed with static and DHCP-assigned addresses. Because the broadband connection was unmanaged, the phone traffic had to contend with our e-mail, FTP and HTTP packets for bandwidth. Internally, the calls were forced to compete with NFS (Network File System)-mounted partitions providing MP3 and MPEG-2 files around the network.
A caveat: Because IP Centrex is still relatively new, coverage areas vary widely. GoBeam offers its service directly only on the West Coast but wholesales to carriers, including Verizon. MCI's coverage is nationwide. ICG falls in between the two, with a service area that cuts a swath across the country. As for pricing, most plans vary by region, and the price you pay will depend on your needs. For example, you can save money by reducing the number of included long-distance minutes. GoBeam also offers an attractive flat-rate option.
After making free long-distance calls to friends, co-workers and anyone else we could think of, we decided GoBeam has the best interface and functionality. For smaller businesses or those not ready for the IP Centrex plunge, check out "Don't Want Centrex?".
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