My carrier is Sprint. is it really necessary to update to new version?

Oh, I get it (after looking it up):

https://www.howtogeek.com/208620/what-is-that-carrier-settings-update-popup-on-your-iphone/

Typically, this means the carrier wants to write updated information to the SIM, but can't do that without your permission. As the linked article says, yes, you want to do that. It's usually to provide better compatibility and/or service with your carrier.

Yes. You should upgrade the carrier version because it affects the technology and ability Sprint uses to provide your cell service. It is separate from iOS versions.

Apple Help article on carrier updates:

https://support.apple.com/en-us/HT201270

marigold16 Said:

"My carrier is Sprint. is it really necessary to update to new version?: My carrier on my iPhone is Sprint. They keep texting me to update my Carrier version. Is this necessary? I keep my iPhone updated to latest version."

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Carrier Sales Promotion?

Is the carrier telling you this? If so it is probably no more a sales promotion, for a deal (i.e. sign up for Unlimited Data, International Calling, etc.). If seems too good of a deal to be true - then it probably is - So, contact you carrier, and don't fall for such promotions.

See this for help. I think they mean for you to update the carrier settings: https://support.apple.com/en-us/HT201270

You can't update a carrier. Do you mean they're trying to talk you into trading in your current iPhone for a newer model?