I aded and app called Network (www.appbrain.com/app/network/de.mangelow.network). On my EVO it shows the IMEI, the phone number and the current network as Sprint. The Optimus S is empty for Current network.
That's odd. There's another app called "Network Info II" that has some good information that normally would be useless. App Brain may not be optimized for a CDMA phone.
At the top of this page, hover the mouse over "My Sprint" and right (secondary) click the submenu "My Preferences" to open it in a new window. Close to the bottom there are options to manage account restrictions like blocking text messages.