[Q] - i9507: No service on KitKat - Can receive calls, can't dial (no service) topic

Hi Guys,

I'm from Australia and recently bought an Optus Galaxy S4 4G. Strangely, the model number is i9507. I double-checked this online and usually weird model numbers are just carrier-spin-offs. So I went ahead to root and flash just like you would with an International i9505.
So far no problems - 4.3.x PA rom works absolutely fine.

BUT:
I've tried some Kit Kat roms recently and they all flash fine but give me 'mobile network not available'. Strangely though, I can receive calls and talk on the phone, but when I try to dial or send text messages, I can't do it. My reception bar is completely empty as well.
WiFi is totally fine, just no data and mobile network

I've tried messing with the 'network operators' setting and if i select my carrier (I have a Vodafone sim) I'll get network reception until I turn off the screen and then my mobile network becomes unavailable again

Not sure what the problem is; modem? APN? or roms not suitable for my phone?

Current info:

ROM - [ROM] KOT49H【4.4.2】 GOOGLE EDITION 4.4.2 by Danvdh, Kryten2k35 & Ktoonsez
Baseband - i9507XXUAMH2
Kernel - 3.4.77--KT-SGS4-KK4.4-TWGE-INTL-01.23.2014---g3367fe0ktoonsez@ktoonsez-VirtualBox #1

I've been flashing for a while now but it's usually just basic stuff so you can probably tell I'm pretty amateur lol.
Any help is greatly appreciated!
Thanks =)

Richard