Custom ROMs only for ICS
If the Phone is unlocked it will stay unlocked.
If you install a custom ROM you will not be able to upgrade using KIES. In fact you will not be able to use Kies.
I strongly suggest that before you root/install custom ROM that you look up how to back up your EFS folder. This folder contains your IMEI in a HEX file
I mean i think it's unlocked for all network because if it is locked to vodafon then i couldn't put other sim card and now i'm using another sim card which is not vodafon,but again i'm not sure maybe the store where i bought it unlocked for all networks,so if i install any kind of ROM's am i going to be able to unlock device ?
Well i read the whole [HOW TO] /efs Folder backup + Restore NV_DATA.BIN and the whole [HOWTO] [REF] [FAQ] [Guides] [Tutorials] Flash/Root/ADB/ROM [MUST READ!] thread i'm learning,by this tutorial flashing device isn't that hard ,but also as @Lexrs sad "you will note be able to connect on Kies" i can't connect now is it maybe the reason because Vodafon or the storte where i bought it flashed ROM?also guy's is there way to check liftimer counter on SGS ?