The issue was in iPhone 4S's GSM chip, which only supported the P frequency band (885-915MHZ), but not the E frequency band (880-890MHz), China Mobile explained.
The problem has now been solved, and all devices manufactured after Feb. 8 fully support China Mobile's network.
For customers who bought an iPhone 4S before that date and are using China Mobile's network, Apple may release a China-specific iOS update in early March to resolve the signal problems.
While this issue may not seem very interesting to those of us outside China, it is definitely a serious one for Apple. China Mobile is the world's largest mobile operator with more than 650 million subscribers; although it is not yet officially a partner of Apple, rumors say this might change in the near future.
Recently, Apple CEO Tim Cook pointed out that China is a very important market for Apple, and Morgan Stanley’s Katy Huberty predicted that Apple could move as many as 40 million iPhones in China in 2013.
[nggallery ID=2585]