I found the solution to be manually editing the APNs in "Settings->Connectivitiy->Mobile Network->APN" and not only selecting my SIM'S APN (the default was some english carrier), but also changing it's type (under 'Settings->APN Type') to "default" (have to type it in manually).
Fixed the problem for me.
# phone/model> HTC One X - EndeavorU
# phone/ROM> ViperX 4.0.6 (Android 4.2.2, Sense 5)
# phone/Kernel> Stock
# phone/Recovery> TWRP 184.108.40.206 Touch Recovery (Repacked with JB kernel)
# tablet/model> Asus Nexus 7 (2013) - 32GB LTE (deb)
# tablet/ROM> SlimKat (Android 4.4)
# tablet/Kernel> Stock
# tablet/Recovery> TWRP 220.127.116.11 Touch Recovery