Thanks - it worked, however just to clarify (I needed some time to understand it).

I looked for config-file with
glocate Mobile
In my case directory with configuration was:
/var/lib/gconf/system/osso/connectivity/IAP/T-Mobile@32@Internet

So the call:
gconftool-2 --recursive-unset /system/osso/connectivity/IAP/T-Mobile@32@Internet
should be not full path but the one below /var/lib/gconf/