DSL services are re-sold by Internet Service Providers (ISP's) from the bigger companies that actually install them. Major providers of Internet services include Covad, Nortel Networks, and, recently, Verizon and other Bell companies. Deregulation of the telephone industry has forced local telephone compaines (IE: Verizon) to open their networks to DSL services, but it is still very difficult for a smaller DSL provider to penetrate this market.
   Most small local ISP's are quite pleased to resell DSL connections provided by larger firms, such as the "big three" listed above. These large installation firms are, in turn, more than willing to turn over customer support obligations to these ISP's.
   Distance from your location to the telephone company's "central office" (or sub-station...) may limit the speed of a DSL connection. (This would not change with a different DSL vendor.)

When choosing a DSL vendor, there are a number of important servcies to look for. The most desirable single feature is 10 (or more) IP Addresses. Each address can be used to support a unique device on the Internet, such as an office router or Email system. Although it is possible for a single TCP/IP internet address to be shared among multiple systems, this is a serious restriction. Be sure your DSL ISP offers your organization many TCP/IP addresses. (16 free addresses appears to be standard.)

Other services are also offered by these ISP's. Some of them are more desirable than others. Typical service offerings may include:

Sophisticated Routers
   DSL ISP's must provide a special "DSL modem" for the connection to the installed DSL circuit. This modem is generally free, or built into an "installation" price, or refunded as a rebate. These modems include Ethernet interfaces (10Base-T, but compatible with most 100Base-TX systems), and can connect directly to your network.
   This is not desirable! With this direct connection, your internal office network is suddenly on the Internet, with no special protection against hackers. To have a defense, and to manage the Internet connection, businesses typically buy and install a special Router device that will protect the internal network from the Internet. This Router would include functions such as Network Address Translation (NAT) and/or a Firewall feature.
   Typically, these routers would work with the Ethernet network itself, accepting the Ethernet signal from the DSL modem and then connecting to the office network "behind" the protective Router with another Ethernet link. However, more and more DSL providers are supplying free or indexpensive DSL "modems" with advanced router features, including NAT and Firewalls. These devices are quite compelling, as they can save hundreds or perhaps thousands of dollars of internal infrastructure setup costs. They can, unfortunately, also add to the complexity of installing "native Internet" devices on the internal network, such as an Email server.

Email Accounts
10 or more POP3 Email accounts. This is meaningless if you are planning on installing your own Email server (IE: MS Exchange), but may be useful for a smaller organization.

Free Web Site
These sites typically include up to 20mb of data storage. Not actually "free", the cost of this service is normally "built in" to the price and adds another $20 or so per month to the cost of the DSL connection. It would be better to deal separately with issues of a web site for your company. Many vendors will offer a web site for $20 or so per month.

Domain Name Support
Issues relating to a custom Domain Name must be managed by the same company that services your web site. However, if you have not yet chosen a vendor for a web site, than this can be an attractive feature. You can register a domain at www.[mycompany].com, and then have sub-domains registered for certain TCP/IP addresses. Typically, this may include net.[mycompany].com for the router, mail.[mycompany].com for the Email system, etc. Sub-domain registration for the TCP/IP addresses the DSL vendor gives you should cost either nothing, or be a minimal charge. This type of function should only be done with your web site ISP. If your DSL vendor is not managing your web site, then don't try to use them for Domain Name services such as these.

Voice-Over-DSL.
This is a powerful technology that may shake the foundation of the local telephone system. A single DSL connection can be broken out into 16 or more "dial tone" connections for standard telephone service. You can then buy fifty or more phone numbers, and assign each number as you please to these 16 channels. Most modern office phone systems will let you use DID (Direct Inward Dialing) technology to assign a unique phone number to every phone in the office. This used to require elaborate and expensive T1 technology. However, Voice-Over-DSL may revolutionise the cost structure of multi-line dial tone. If your office has five or more telephone lines used for voice calling, you may consider investigating a DSL ISP that offers Voice-Over-DSL service. This type of service may not be compatible with an data connection, however, so you may need a separate DSL link for Internet access.