yes, you can add the insurance regardless where you got the device...
just a heads up when buying a phone from craiglist or ebay. Make sure the ESN is clean. If the device is brand new, then it should be fine. but if it was used at any point and they didnt finish paing their bill, the device wont be transferred to your acct until the debt is settled with sprint.
If the seller gives your the ESN, you can call sprint or do the online chat to check if its clean/clear!
Good luck!
Thank you,
I already bought the item and it is brand new, sealed in Sprint retail box and with a clean ESN.
I will be deactivating my HTC Touch semi-Pro and activating my Palm Pixi by the end of this week

EDIT: Oh and I got it for $300 no new contract necessary....beat that Sprint!