1. A Verizon phone has the Verizon number programmed over-the-air(the *22890 you punched in the phone activated the phone and programmed it). For PagePlus the Verizon side would work in the US on Verizon and roam domestically at higher rates, and possibly roam internationally in Canada, Mexico and Bermuda in CDMA mode. I say possibly because people I've known that have roamed internationally using PagePlus have had mixed results. But if these three international destinations are where you primarily travel than you can get probably get away without a global roaming phone.
2. A Verizon phone that also has a sim slot for GSM global roaming uses a separate sim chip that is in addition to the CDMA programming mentioned above. Generally the phone comes with a Verizon/Vodaphone sim chip that has fairly high international roaming rates. To use a different sim chip you need to unlock the phone. You could try Verizon Global Service or PP customer service, but I can't guarantee favorable results (but they might provide the handset subsidy unlock code for free). An easier solution is to have it unlocked for a small fee by going online to a HoFo or ebay dealer that does unlocking or to a local independent cellphone store that has unlocking services. It's a fairly simple and inexpensive procedure to unlock most handsets.
3. Once the handset is unlocked, you can insert any GSM sim chip. You may need to change a menu setting to select the GSM chip rather than the Verizon/PagePlus CDMA default.
4. What international sim chips to use:
A local sim chip is cheaper. Can be bought in advance of travel from some dealers on ebay and elsewhere or at your destination at the airport or a cellphone shop. Use and toss. Or refill online if you need to keep the sim chip for future trips. I have a Bermuda Digicel sim chip purchased inexpensively on ebay I keep filled up for trips to Bermuda and sister Digicel countries in the non-US Caribbean. I add BM$10 every 60 days, and I have enough balance when needed for my next trip.
A callback sim chip (ekit Simple Calling service, Telna, Blu, Telestial Passport, etc.) is more complicated. They usually have a domestic dialing side for US and Canada travel, and an international call-back number side for elsewhere that you select as needed. Domestic is direct dial-out; international is dial out, the call disconnects, a message comes up on the screen, than the phone rings and it connects you to the party you have dialed after a voice message says what your minute balance is for your particular calling destination. I currently have an Ekit Simple Calling service sim card (cheapest bought over ebay) with a New York and a UK number on it...used it most recently for a multi-week trip to the Cayman Islands in Dec./Jan.). Rates are often inexpensive per minute but vary by destination; check your itinerary against various call-back sim cards to see which are priced best for what you need.
Also note some US carrier prepaid sim chips have limited international roaming capabilities. AT&T GoPhone has very competitive prepaid roaming rates in Mexico and Canada (think 25 and 39 cents respectively per minute). T-Mobile Prepaid can roam in Canada, Mexico and in some other foreign countries...but please note their foreign prepaid roaming rates outside North America are rather expensive.