Can i use my unlocked iphone 3gs to metro Pcs service?

Well since now i've heard that metro has the "bring your own device" service, i've been hearing. That you can use iphone 4, 4s, and iphone 5 to metro, but never found out about the older iphones so can it be possible to use the older iphones to metro?

No. The 2G, 3G & 3GS were GSM only phones which will not work on metroPCS' CDMA network.

Not if the phone is not CDMA.