Originally Posted by DevonBloke:
“But surely if you have data then it must say "Vodafone 3G" at the top of the screen doesn't it?
If there was no signal, you wouldn't get any data connection.”
Not entirely correct.
The way mobile phones "register" on the network on pre-4G networks works like this
There are two separate logical connections - one on a circuit switched and one on a packet switched domain. One provides the phone with a phone number allowing it to make and receive calls, the other provides it with an IP address allowing it to make and receive data. This is how mobile data can be turned on and off independently of your phone calls. Both go through the same, physical 3G modem.
It's like logging into GMail on your computer for emails and also logging into Skype to make voice calls. The two operate separately and independently.
Most phones will automatically connect CS (voice) on startup and then optionally PS (data) when needed. Hence, CS should always be active, while CS+PS is optional extra - on handsets.
Most phones, then, also use the presence of a successful CS registration to decide whether or not to display signal bars or "No service" - in this case it really only refers to
voice service. However, it
is possible to get PS (data) connections on their own, without CS (voice) at all. There are both phones and SIMs that only support data with no voice at all.
Now because it's possible (both intentionally, and due to a fault) to get PS without CS, if your phone is one of many that only considers CS to be "signal" it'll display no signal or service in the presence of a PS only registration. Simples.
Long story short - your phone is operating in "data only" mode, and not displaying signal bars not because there's no signal, but because it can't get a voice connection. This is a common phenomena on phones that aren't intended for data-only connections.
As for possible causes, the three I can think of are:
1) Vodafone make a lot of data-only SIM cards and may have sent you one by accident (unlikely)
2) The handset might have been set to PS only mode (also unlikely)
3) A network or account glitch that hasn't registered your voice line properly to your SIM (probably the most likely). O2 had a couple of these a few years back on a nationwide scale - people could get data but no voice causing phones to display "No service"
So I'd try, in order:
a) A different SIM
b) Calling Vodafone and asking them to replace the SIM
c) Factory resetting the phone.
