If things haven't changed anyway, AFAIK you cannot use the tracfone SIM inside a Palm Treo, even if it's unlocked. The Palm Treo does not have the proprietary firmware/software required for use w/ the Tracfone SIM. FWIW, some folks flash (change the entire firmware) their tracfone handsets for use w/ other wireless carriers. You will essentially have to try another pre-paid service, such as ATT or T-Mobile (being the ones using GSM/SIM cards). If T-Mo gives adequate coverager, just walk into a T-Mo store- they will normally give you a SIM for their pre-paid service. ATT can be a mixed bag in this regard, but they offer both PAYG (pay as you go) and PYP (pick your plan). Places like Target/Wal mart sometimes sell one or the other depending on where you are located. More info on both here:

http://www.wireless.att.com/cell-phone-service/go-phones/index.jsp?wtSlotClick=1~00107M~0~1&WT.svl=calltoaction

http://www.t-mobile.com/shop/plans/Prepaid-Plans-Overview.aspx?WT.mc_n=PrepaidOverview_PlanFirstTile3&WT.mc_t=OnsiteAd

hth,
Pedro