as you do not require a built-in modem to connect to a DSL or Cable line.
Usually the built-in modems are just for a dial up telephone connection.
When you order your DSL service from your local supplier, they will supply you with a DSL modem. If you tell them beforehand that you want a Wireless modem, they should be able to supply you with one of those instead of the regular wired modem.
Just a thought. Do you already have internet service at your place?
I'm planning to buy a late-2009 or mid-2010 iMac. As I understand it, they have no built-in modem. Do I need to buy a DSL modem for a DSL connection and a wireless modem for a wireless connection?
Also, I would welcome any recommendations or caveats re specific models.