Question 2G/3G switching ways with ROOT

I have a stock jelly bean rom for my nexus s and I want to switch 2G/3G without using an accessibility tool like Tasker provide.
Surfing on the internet I have found a couple of methods I can use to do this switch but no one of this works, what I do wrong? (examples to switch to 3Gl)

am broadcast: (as seen here)
am broadcast -a com.android.phone.CHANGE_NETWORK_MODE --ei networkMode 0

sqlite3: (as seen here)
sqlite3 /data/data/com.android.providers.settings/databases/settings.db
insert into global values(null, 'preferred_network_mode', 0);
.exit

With am broadcast doesn't change anything viewing the "Only use 2G" checkbox in the android settings. Instead, using the sqlite3 method in the settings.db file there isn't a global table and I can't find the preferred_network_mode option.

What I do wrong?