UPDATE*
firstly flash your k800i to
K800_R8BF003_MAIN_GENERIC_WI_RED52
K800_R8BF003_FS_EUROPE_4_RED52
HB1-06_Generic_CDA102568_13_R4A_GENERIC_EUROPE_4
(which can be found in topsony)
then use remove sim lock patch for k800i R8BF003 (from the link below)
http://www.megaupload.com/?d=E2U2ZWT0
(NOTE: i am not responsible of what can happen to your phone so do it at your own risk!)