Nexus s 4g flashed to Metro, but cant activate it

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http://forum.xda-developers.com – I bought a nexus s 4g from someone and they had it flashed to metro previously and just removed their account 5 days ago. When I call 611 it goes to metro...but when I took it into Metro corporate store, the guy said I need to take it to a store that does flashing and have them do some programming. what can I do without spending more money than I already have? (HowTos)