I have a Samsung Captivate (Galaxy S) and I have an AT&T plan that includes tethering. I can turn on the Mobile AP hotspot and then other devices can connect to it.
However, after several minutes, the Mobile AP turns itself off. If I manually turn it back on again, it works fine again, but this gets pretty annoying.
Is there any way to make it stay on, or to lengthen the time it will stay on?
Go to your WiFi settings and hit the menu button and click the Advanced menu item. Check the WiFi sleep policy, and if it isn't set to Never, try setting it to Never to see if this resolves the issue.
I had the same problem and solved it on a Samsung Captivate (Galaxy S - SGH-I896) with Rogers in Canada. The problem was an annoyance at first (disconnecting every 10-20min) but got worse one day when it stopped allowing tethering altogether with a message "This Account is not configured for Tethering. Please Contact Rogers Customer Care." Calling Rogers solved nothing as the problem is not at their end.
The problem stemmed from a bad version/copy of a file /system/app/TetheringManagerRoger1126.apk
I first rooted the phone using SuperOneClick: http://forum.xda-developers.com/showthread.php?t=803682 (Had to turn off my antivirus to unzip the files and they contain linux exploit code.)
After ensuring I had successfully rooted my phone, I got the app: "ES File Explorer" from the market. In that app, I had to go to Menu->Settings and turn ON "Root Explorer" which required SuperUser permission. And turned on "Mount File System" as writable. Once that was done I could browse to the: /system/app/TetheringManagerRoger1126.apk file and just rename it to .bak
That solved both the error message and the constant disconnecting and I can tether indefinitely on the phone now.
I assume that if you're on AT&T, there is a similar TetheringManagerApp file that is the cause of these problems and renaming it should fix it.
Hope that helps.
