Thanks for the reply but in data sheet it is given as the following phones alone Cisco Unified IP Phones 521G, 521SG, 524G, and 524SG.

And light me in ordering process to:

UC520-24U-8FXO-K9, it come with 24 user licence file, when I am ordering 7942 IP Phone do I need to get phone licence file along with IP Phone or licence is not necessary since I got Licence for 24 users.

With UC500 if I get the following IP Phones 521G, 521SG, 524G, and 524SG, I hope I dont need license file, please correct me if my understanding is wrong.

You're probably misreading the data sheet, all current phones are supported.

You do not need to order any other license with UC520. Beside, CME phone licenses are pieces of paper, not files.

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With UC500 if I get the following IP Phones 521G, 521SG, 524G, and 524SG, I hope I dont need license file, please correct me if my understanding is wrong.

That is correct you don't need a license with the Cisco 500 Series IP Phones