Buying SIM for T-Mobile & keeping ST phone number

[Rebel60]

I just bought a used Samsung Galaxy s II for T-Mobile. I want to buy the T-Mobile SIM and transfer my existing Straight Talk phone number to the Samsung Galaxy. Not sure if the Galaxy is "unlocked" Do I order the SIm & then call CS when I am ready to switch phone number from 1 phone to the other. How do I tell if the phone is unlocked?
Also if the service is terrible in my area can I sell the SIM to someone else? Is it transferable or is it tied to my account and location.
Will there be a SIM to use with Verizon? My current CDMA phone uses Verizon & I get really good service.

[Shelly_ST]

Hi, Rebel60. My name is Straight Talk Shelly and I will be addressing your question. In order to determine if the phone is unlock you may check the user guide or the activation guide that comes with the phone. To make sure you get the correct type of SIM card for your phone please log on to www.straighttalkSIM.com. Once we transfer your phone number to a different SIM card, the current SIM card will be deactivated, hence, it can no longer be reactivated with a new number. There are no SIM cards available for CDMA phones. I believe this answers your question. It’s been a pleasure helping you. Have a good day.