Yes you can always pay full retail for a device and not have your contract extended.
I can see how activating a different phone may bring some confusion with regards to your contract. In addition to Tidbits post (Thank you!) I'd like to confirm that if you buy a phone listed as a No Contract Verizon from a third party you will be able to activate on your current Family Share plan on your existing line as long as the ESN is not included in the lost/stolen list. You can confirm phone activation eligibility online at this LINK.
I understand that you are eligible for an upgrade sometime later; please be assured that activating a device obtained via a 3rd party does not affect your contract term or your future upgrade eligibility, You can activate/switch phones online at your convenience.
Buying a Verizon Wireless phone from us at full retail price does not extend, breaks or modify your current contract. Your 2 year contract remains unaltered even if you replace your phone with one obtained via a third party; keep in mind that depending on the type of phone you activate you may need to add features to your account (i.e. replacing a basic phone [no need for data plan] with a Smartphone which require a data plan feature to be added) but adding a more advanced device does not require a new contract and does not breach the current contract.
If you get a 4G LTE phone from a third party you will need a SIM card (we provide free of charge) to activate and you can order SIM card online if you login to your My Verizon account or by calling 800-922-0204 when ready to activate. You will not incur any fees for replacing your basic phone with a 4G Smartphone; however keep in mind that you will have to add a data plan feature for your Smartphone when you switch the device.
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