Using phones from other carriers

Quick question. My sis-in-law updates her phone every 6 months. She uses Verizon.

Can I use her old phone on the T-mobile network by just swapping my SIM card into her old phone? I rarely update my phone (only when I can do it practically for free), and her old ones are nicer than my current phone. Thx!

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First of all, Verizon phones do not use sims cards, well at least not yet...
second T-Mobile is GSM and Verizon uses CDMA technology, not compatable...