I bought one from bell Canada, and I can't put in a SIM card from any other service provider. Does anyone know how to unlock this phone?
To unlock your phone, use GalaxSim Unlock.
You need root for this app. If you don't have root, the app will give you instructions on how to root your phone.
You can unlock your Samsung Galaxy S using unlock code .You can get unlock codes from the network provider or online vendors like Unlocking4U.com . But, Most Network providers will provide the unlock code only if the contract period is over . From Online vendors you can get the Unlock code at any time for a small price.
First you need to know if your phone is CDMA or GSM. If it's a CDMA phone then it cannot be unlocked.
GSM phones can be unlocked to make it work with other networks. If you want to unlock your phone for free you can root your phone but it is at your own risk. Also rooting voids your warranty.
Safer method is to get an unlock code from the unlock code providers like http://www.samsungsimunlock.com/ There are other unlock code providers like http://www.unlocking4u.com but there are slightly expensive.
Unlocking phones is restricted in some countries. Recently US passed a law where unlocking phones is illegal that are manufactured after Jan 26th 2013. Phones manufactured before that date can be unlocked. Please check your local laws before unlocking.