In small businesses you will often have the ADSL broadband and telephone line from the same connection. You may also need to setup an EPABX on the connection to share the phone line. For example we use an EPABX to provide 16 internal connections over two external lines, one of which also has the broadband. Here is how you can easily setup both EPABX and your ADSL connection on the same line.
The splitter should be used ahead of anything else. The ADSL line coming out of the ADSL splitter (will be appropriately marked on your splitter) should be connected to your broadband router, while the normal telephone line (should be marked on the splitter) should be connected directly to your EPABX as one of the external lines.
That was simple, no?
I am using this setup for a long time without any issues. I use ACCORD EPABX and DataOne Broadband on the same line.
PS. I also have couple of wireless routers allowing laptop connectivity, sharing two broadband connections, one of which is mentioned above.