I'm frequently getting the "Cannot Activate Cellular Data Network" error, or otherwise can't access data on my iPhone 4S (AT&T). I'm sure a lot of it is because my office has a fairly weak AT&T signal (Midtown Manhattan). However, what's odd is that even after I get back into a strong signal area, it often won't connect to data unless I reset the network settings. Also, I'm finding it difficult sometimes to connect to data even when the 3G light is on and it shows 4 bars (or an RSCP in the -70 to -80 range in Field Test [enter *3001#12345#* and press "Call" on the keypad]). It will attempt to connect, or to download a message, only to time out later or just keep fetching unsuccessfully. Does this sound like I have a defective cellular data modem, or is it just AT&T being AT&T in NYC? My Blackberry was able to connect from the same office, so in theory the UMTS data signal is there and strong enough.