Well, you actually did say that it would work with "all 3G networks". It's a post on the first page but that doesn't really matter. 🙂
I see that you were unable to find where that link suggested an incompatibility between my iPhone and China Unicom's 3G network.
Well according to Apple, my iPhone supports these radios:
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
GSM/EDGE (850, 900, 1800, 1900 MHz)
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
According to China Unicom's site (http://eng.chinaunicom.com/international_roaming/roaming_faqs/) their 3G network is a WCDMA network. That doesn't seem to be listed above.
And, as I have stated multiple times before, I have already gone through the proper procedures to request an unlock from AT&T. It was purchased off contract and I paid the full retail price.