My phone had ICS on it out of the box. My MediaNet data plan provisioned SIM worked with the phone. However data tethering would NOT work although the same SIM in my Xperia Ray running Gingerbread would allow tethering. Also data speeds were averaging only 2Mbps which was very similar to my Xperia Ray but the Acro S is capable of 14.4Mbps vs the 7.2Mbps of the Xperia Ray.
It appears that there is something about the ICS update (and AT&T) that prevents tethering when using the AT&T MediaNet data plan vs. a true smartphone data plan from AT&T. The same thing happened with loss of tethering when I updated my Xperia Ray to ICS. I had to send it back to Sony to go back to Gingerbread, after which tethering worked again.
The phone has a default mobile network setting to use the wap.cingular APN. So I had my SIM re-provisioned with a 'true' smartphone data plan but tethering still would NOT work. Also data speeds were still slow. Since AT&T does not sell the Xperia Acro S, you get provisioned with a generic smartphone plan were you still must use the wap.cingular APN. Tethering is allowed if you are provisioned for it, but it would not work because of the T-Mobile operator settings that were 'stuck' on the phone (see last tip at end of this post for dealing with this).
I tried the Settings menu option under Xperia ... to get mobile operator settings and noticed that it pulled in the phone APN settings. This is what the iPhone and many other AT&T phones use. But I could not connect to data (got voice only). The generic smartphone data plan does not allow you to use the phone APN.
So I had my phone provisioned as if it was an iPhone 4S. That allowed me to use the phone APN. Data speeds instantly were in the 5Mbps on average and I've seen speeds up to 8Mbps. Never saw anything close to this using the wap.cingular APN. Tethering now works too once I followed the below 'Last Tip'. (what a mess)
Last tip ... there was a confirmed bug in the ICS version shipped on the phone where the default T-Mobile operator settings could not be deleted. Even after updating to the latest ICS build. I found that you MUST factory reset the phone after the ICS update and then the T-Mobile settings were automatically removed. You must get the T-Mobile settings off the phone in order for the above iPhone data plan to correctly work for tethering and optimal data speeds.
Regards,
Bob H
