[Question] 3G and custom roms

[HappyUser]

Hi all
Can anyone tell me why 3G just won't work on some ROM's?

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 "choose carrier manually"...

I then have tried different ways to make it work. I have tried to copy/paste 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...?

Is it not possible to customize the custom ROM i like, with the working 3G settings from my other ROM?