as far as i know first transfer ur msgs from nokia 6630 to comp using pc suite....
but donno much abt transfering it from 6630 to p990i.... both are on same os but different interfaces.... if u wanted to transfer from 6630 to 6600or any other symbain phone which is same version as 6630 then u can copy msg's to memory card and then access it in other symbain phone which has option to store msg's in memory card.... any problem regarding copying msg's p.m me .. i'll help out..