Maybe a month ago I set my device to use only wifi for data connection. Now, with a bigger data package, I try to find where I can put back 3G for data connection.
I didn't do any fancy tricks nor # 4036# ... things.
Any ideas ?
You can turn 3G data back on through 'Settings'.
Now you're phone should have both 3G and WiFi enabled. If it can connect to a WiFi, it'll use WiFi; otherwise, it'll fall back to use 3G.
edit: as Seth pointed out below, these instructions may differ slightly between android phones (but should be relatively similar). Instructions above are for the HTC Desire.
I am using Samsung Nexus S. I think most of the android phones are very similar. Please follow the following steps;
Now you could enable "Data enabled" option, which is the first option could be selected.
Then, you could access the network through wifi or 3G.