[Question] 3G and custom ROM

[HappyUser]

Hi, I have posted a similar thread i the Star S5 forum, my question is :

Can anyone tell me why 3G just won't work on some ROM's, or how to build/customize a ROM with 3G settings/files from another ROM?

I'm currently running a custom/updated rooted ROM, [Only registered and activated users can see links Click here to register] and my 3G Network works fine here. I then wanted to try out another custom ROM [Only registered and activated users can see links Click here to register] but here, everything but the 3G Network are working flawlessly... - I simply doesn't have any carriers to choose from in "select carrier manually"...

I then have tried different ways to make it work. I have tried to copy/paste different/several modem.img, I have tried to install SD update via recovery etc.
The baseband ver. on my working ROM are MOLY.WR8.W1248.MD.WG.MP.V7.P1, 2013/04/10 00:41
Why does it not work when I transfer it to the ROM where 3G does not work? What needs to be done differently...?
Does NVRAM also have something to do with it?

Is it possible to customize/build the custom ROM i like, with the working 3G settings from my other "working" ROM somehow?