I'm not sure if this'll work but I think you can export your contacts to .VCF files (using PC Suite, not Ovi Suite)
there you'll find when a specific contact card created (I think )
BEGIN:VCARD
VERSION:2.1
N:Gump;Forrest
FN:Forrest Gump
ORG:Bubba Gump Shrimp Co.
TITLE:Shrimp Man
TEL;WORK;VOICE111) 555-1212
TEL;HOME;VOICE404) 555-1212
ADR;WORK:;;100 Waters Edge;Baytown;LA;30314;United States of America
LABEL;WORK;ENCODING=QUOTED-PRINTABLE:100 Waters Edge=0D=0ABaytown, LA 30314=0D=0AUnited States of America
ADR;HOME:;;42 Plantation St.;Baytown;LA;30314;United States of America
LABEL;HOME;ENCODING=QUOTED-PRINTABLE:42 Plantation St.=0D=0ABaytown, LA 30314=0D=0AUnited States of America
EMAIL;PREF;INTERNET:forrestgump@example.com REV:20080424T195243Z
END:VCARD
i suppose the REV entry is the last time you make changes to the contact
oops.. I remember seeing this on exported VCF from symbian phones. I don't expect that this tag is omitted on N900
oh there actually is
try this
vi /home/user/.osso-abook/db/addressbook.db
you can find REV tag there, but don't know whether it's actually valid for determining which contacts created before/after other contact
due to no berkeley db client i know running on maemo device, i can only think of using vi to open the file
or you can copy the db to your pc for more comfortable reading
)
111) 555-1212