I am using an o2-UK iPhone running 3.0 Beta 3 and also have a blank Network Data Settings page. So it's not just you.
You could try dropping back to Beta 2, using the DFU method people are using to get back to 2.2.1. BUT to the best of my knowledge there are validity periods on the betas, and Beta 2's expires in just over a week. So you would have to choose between Beta 3 and 2.2.1 by the end of the month.
I've been having a rollercoaster couple of hours. First of all I try to put my phone into recovery mode. I then get the dreaded pink screen of death instructing me to connect the phone to itunes. When i chose to restore, it would not detect my iphone any longer. Then after about an hour of trying to get into DFU mode, but not really making any difference I realize how to restore from an IPSW by clicking 'alt' and restore at the same time. This seemed to work and restored my phone back to Beta 3.
The first thing I obviously attempted was to access data using the cellular network, which failed - hence my phone no longer has the correct APN settings. I tried to change this in the settings on the phone, but it still has a blank screen on this option.
I then decided I would restore from a BETA 2 IPSW file, as I know you can input your own APN settings on BETA 2, and I found it generally stable enough to use until BETA 4 comes out. However when I tried this restore it took me back to the dreaded Pink screen of death.
I am now trying to get BETA 3 back on the phone again, and it is restoring I type. I will keep you updated.
My question now is, is there a way I can manually change the APN settings on the phone without accessing the Cellular Data Network settings on the phone?
Of course this could all be in vain if I get that screen of death agaiN!!
*****UPDATE*****
OK I can confirm that I can restore back to BETA 3 and the phone is functional as it was before my nightmares. Anyway the Cellular APN settings are still not working, so I can only use data at the moment in a WIFI area.
I have done a bit of reading about changing your carrier IPCC file to change the APN settings, it all seems simple enough but I can't locate the IPCC file. It is supposed to be in: ~/Library/iTunes/iPhone Carrier Support folder. The problem is that I do not have this folder.
It seems my last resort right now would have to be DFU mode back to 2.2.1 which in my opinion would not be the end of the world. I am now really worried whether it will work or not though!
Also I notice to get back to 2.2.1 you have to Jailbreak, which I don't really want to do either. Once you have Jailbroken your phone, can you unJailbreak?
So many questions!!
Thanks for your help so far guys