Any Sprint/Nextel phone that does have a SIM card is using iDEN network, not GSM and it will NOT work in a GSM device
Copied from Phonescoop.com:
Newer iDEN phones use a SIM card that is compatible with GSM phones for overseas roaming. However, iDEN is a very different standard from GSM. Most iDEN phones are not compatible with GSM networks, and GSM phones are not compatible with iDEN networks.