i bought with 2 year plan at $648 for M1.
Singtel is $798 with 2 year plan and Starhub is $610 after $88 Hubber Bonus off if you have maxonline or cable TV. Starhub promotions until 31st March.
Islandwide for i600 only the main starhub shops at plaza singapura etc. have them. Singtel all have stocks but nobody buying them because the price is too high. M1 i got it from an exclusive distributor at the Suntec, the Handphone Shop. M1Shops all no stock.
i600 most probably will get an upgrade (free or not im not sure too) to windows mobile 6 when it releases.
The treo 750v you mentioned will also most probably get OS upgrade too.