First of all, send an explanation in writing to Sprint, stating that you are the person residing at this address, not the one they are looking for.  And request a written response from Sprint.  By law, Sprint is obligated to answer your complaint, maybe in 30 days?  I forgot what the limit is.

Second, send a complaint letter to the collection agency, stating that it is an erroneous collection, and you are working with Sprint to clear this matter.  Also ask the collection agency to cease all communication with you, as prescribed under the Fair Debt Collection Act (FDCA). 

By law, the collection agency must comply and cease contact with you within 30 days of receiving your letter.

keep a copy of everything you send, and mail out the letters certified with return receipt and keep all receipts.