If you have access to a T-Mobile or AT&T sim card just try using it in your iPhone to see if it works. If it does then you know the info stated on other sites is true. I know originally it was stated that iPhone 5's shipped from VZW were unlocked but no info provided on if those shipped from Apple are also unlocked.
How have you checked?
According to Apple's website, US iPhones will be locked to the carrier within the US.
You would, however, be able to insert a SIM card from a foreign carrier for use internationally, and some have reported that with an international SIM you can also roam on other US carriers.
There are those that say the Verizon iPhone 5 is NOT locked to Verizon as a US carrier, though I have not seen anyone who has said otherwise from experience. They only point to websites stating about "theoretically" being unlocked.
Have you tried an AT&T SIM in your Verizon iPhone 5? An international SIM?