If you program it in as a number for a contact, you can use the letter "w" or "p" in the dialdstring for wait or pause. The first waits a few seconds, the latter pauses until you hit the talk button.

I would create contact "Conference" , number 1800NNNNNNNNp1111p2222
where 1111 is the conference number and 2222 is the pin.

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