1 company that has 3 brand names

[plim81]

Mitel 5000

customers are calling into our company, but we have 3 brands and we would like to answer the phone accordingly.  what do we need to do this?

For example:

1-800-555-1111  ABC Company
  When a customer dials this ABC company # above can ABC company show up in the caller ID, so that our employees answering the phone call can say 'Hello, thank you for calling ABC company'. 

1-800-555-2222  XYZ Company

1-800-555-3333  EFG Company

Or are we going about this all wrong and we can buy equipment that can make this happen?

[DND ON]

What type of trunks do you have? How are the toll-free numbers routed?

[dwayneg]

Are you trying to identify the company during ring in or throughout the calls progress?  In other words, does everyone who touches the call need to know the company or only the first person who answers?  Different methods for each.

[magnus]

There are 2 ways I can think of off the top of my head.

Method 1 (assuming PRI)
Route the call to a CRT then to a CRA based on number called and then hunt ground with the Username of the company.
The name will show up on the persons phone

Method 2
Use Phone manager
Setup the banners to pop up with different colours for each company so the person answering has a visual cue.

[dwayneg]

If you only need to identify to the first answering point you could build a phantom ext for each, then represent those phantoms with SECONDARY CALL KEYS on user's phones.  The beauty of this is that user must press the key to answer, making sure his mind is in the right gear.

[DND ON]

Until the OP comes back with more info, we can't begin to answer the question.