Trying to use a Samsung Galaxy S device coming from China or Korea in Russia lead to the observation that the quality of the connection to the mobile network is much worse than on Samsung Galaxy S we used previously (which was bought in Russia).
I have installed CyanogenMod 10.0 on the device in the hope that the mobile network connection quality would improve. But that doesn't seem to be the case.
Now I see information that there are different firmware available for the modem; one should try to flash them to get modem working well in a specific region --https://android.stackexchange.com/a/44021/13117:
Well, I guess you should flash another modem file, which is working well for your region/carrier (use google . A modem file defines how the radio part of your phone works, it has an influence on signal strenght/network speed (and might have influence on battery life, too).
and http://forum.xda-developers.com/showthread.php?t=1158783 lists a lot various modem firmware for the device.
Which one to choose for Russia, Moscow (Megafon mobile network)?
(The one that was working bad for us is XXJPK, and--on another device from China or Korea--SPJG2, which also has bad/unstable signal, but not as bad as XXJPK. After the installation of CM10, XXJPK on that device was replaced with XXJVT, which again has very bad signal.)