I have had this happen on my 4s (with no JB obviously). It drops 3G data, but the Network name still says 'Telus' just no '3G' beside it. No WiFi either (I don't know if it was because of no networks close enough, or if WiFi just died along with the 3G data at the same time) A full hard reboot fixes it... and if I don't manually do it, the phone will go to black screen... then apple logo... rebooting itself spontaneously. In the Diagnostics... I notice a panic.plist file each time it does this with 'IOUSB' seemingly as the reason for the kernel panic. But it all started with that message popping up 'No DATA service'
Now, my problem is this: kernel panics are supposed to be 90% hardware related. I bought the extended warranty from Future Shop which is supposed to include straight exchanges. Problem is, this seems to be a random occurrence. FS said that they NEED to see it as it's actually happening... after they restore to factory. Since it's random, happening about once a day for me, that would mean them restoring (to 5.0.1 obviously) and me waiting all day at the Future shop store - and even then, if it happened while they were looking away helping other customers, then it doesn't count!! WTF?? The panic.plist files are NOT GOOD enough for them!

I was so mad! Their extended warranty is worthless and I paid over 300.00 for it - and I am now stuck with a lemon!!! I have no land line, only a cell so I can't afford to send it away to Apple and be without the phone.....
Anyway, my point is, this issue MIGHT be hardware and not software related. I also don't know which phone and which firmware you are currently on (you didn't say)