I think it is 800-333-DISH, but the number is located in the receiver manual, somewhere in one of the menu, and when trying to select certain channels it will tell you to call the 800 number. Then just follow the prompts with a touch tone phone.
Just be prepared to set up an account by giving them a Name, SSN, Phone Number, Service Address with Zip Code, and if different - a Billing Address. They will also tell you to go into the menu to retrieve a couple of numbers from the receiver. They will probably ask what type of Dish antenna(s) you have, especially if you are looking for HD, Foreign Languages, etc...
If your Service Address Zip Code covers muliple locations, such as crosses two counties, then they may ask you what part of the Zip Code you are in. This is used to determine what programming (such as DNS, Locals, etc...) you can receive and which black outs apply to you.
PS -- They may also want a credit card number.
And I believe you are already aware that you need to be able to lock onto each of the satellites you are planning on receiving signals from.
If you have everything correct and having trouble with the CSR saying it won't work, just hang up and call back to start over.
Good Luck.