This is a problem with AT&T. I'm running 4.4.4 Android on a new Note 4 and discovered that Google Voice wouldn't run on the phone. I suspect the issue is tied to AT&T's implementation of their Visual Voicemail.
After spending a few calls with AT&T Tech Support, I was able to get my Google Voice to work by using the Call Forwarding Settings of "Forward When Busy", "Forward When Unavailable", and "Forward When Unreachable" to be set to my Google Voice number. The problem is that the Note 4 has the bug you mention. It's not possible for the user to access the settings on the phone without getting the "Network or SIM card error" message.
AT&T Tech Support can manually configure these settings, but this will only help if you don't change the settings often because a call to AT&T is required. I'm hoping they fix this bug in the Lollipop build.
Be careful when calling AT&T Tech Support, the first two times I called, the Tech Support Agent had no idea that this type of Call Forwarding Settings were configurable.
For the 3rd try at calling them, I got someone more knowledgeable who first reset my voicemail to "Basic Voicemail". This is done in the AT&T system, not on the individual phone. Once that had been done, I then had to "activate" the Basic Voicemail by configuring my box. As soon as that was done, the AT&T rep was able to go into the AT&T system and manually configure the three Call Forwarding options that I wanted.
It was a huge pain to go through, especially because all I wanted to do was use Google Voice which has worked on AT&T Samsung phones going back to my first Galaxy SII.
My phone still shows the "Network or SIM card Error" whenever I try to access the Call Forwarding Settings, but at least I was able to get the Call Forwarding configured for my Google Voice to work again.
I don't know if this info helps you out, but I wanted to pass it along.
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