I am thinking about switching my cell phone carrier from T-Mobile to Sprint?

You can't switch your network carrier from T-Mobile to sprint.Because T-Mobile is GSM based and sprint is CDMA.
But you can switch other GSM network.If you are interested to use other GSM network service means,you will need to unlock your phone.For unlocking you can approach your service provider or else try to buy an unlocking service from any one of the online unlocking service provider like ProUnlocking.com Here you can unlock your phone at low cost.I hope it will be very useful to you.