that is no much different between DZIF1 and DZIA5, just DZIF1 is a updated ROm with some new picture and icons.
u no need to change anything, upgrade to other official ROM didnt made any change. unless u want try CUSTOM ROM.

i900DXIF1/DZIF1 the first one is the content of the ROM, and second is the release of the ROM, if not mistaken.
there may have i900DXIF1/DXIF1 ROM in some country because DZ is for SG,MY and DX is for SEA country such as Indon and Philippine
SG and MY version is english ROM with preinstalled PlumSIP 6.0 in ROM for Chinese input.

This also caused that u can't update to PlumSIP 6.1 directly, need to manual delete something anf left so rubbish in windows...
however PlumSIP no have frequent update for WM phone as the company had been take over by Baidu and release Baidu input.

DZIA5 have a bug for online widget which when u on the Motion sensor together, it will cause the SMS notice not functional. u can try on urs, see got such problem or not, as my friend use the same ROm as urs, said not such problem.

BTW for those like to try Infinitine Today which I introduce befoe, the had release version 5.0 in English version. try have a look at
http://bbs.domobi.net/thread-7456-1-1.html but this website is CHinese one.. hehe

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Added on December 12, 2009, 1:51 pmSTEP by STEP update ROM is on the first page, plz read through it first.