The Number You Dialed Is Switched Off…

Lately, calls going through to my Globacom mobile line has been something of a “hit and miss” affair. Naturally, i blamed it on the inefficiencies of the mobile network and prayed for the best. But i became a little worried when, curiously, my wife’s line works perfectly well even though we both use the same network.

I use an iPad phone, which shares most of its phone features with the iPhone. As the phone feature of the ipad is not exactly common place, I decided to search on the internet for the iPhone and “unreacheable calls” issue. My findings were very revealing and disturbing. The UK mobile network, 3, aptly captures the problem in one of its forum threads.

Below is an excerpt;

A problem that many people report with the iPhone is incoming calls going straight to voicemail without ringing, and delayed incoming texts, both despite strong signals. Although a LOT of people complain about this issue, and blame the iPhone,  little information exists about what really causes it or what can be done about it.

If you’re on 3G you can receive incoming calls and SMS messages while you are in the middle of using 3G data – simultaneous voice and data is part of the 3G UMTS specification. So it should never happen on 3G, unless some other problem is involved. However if you are on GPRS or EDGE (E) the specification does not allow for simultaneous calls and data – if you make an outgoing call an existing data session will be terminated until the end of the call – the call takes priority.

But what happens if you’re already using data on GPRS/EDGE first (browsing a web page, checking google maps etc) and an incoming call comes in, will you receive the call or not ? Probably not. I have SIMs for all the networks in the UK and so far I’ve tested Orange, 3, (who use Orange for 2G anyway) O2, and T-Mobile, and they ALL go straight to voicemail as if the phone is turned off if I call the phone while it is using GPRS/EDGE data. SMS messages don’t come through until later either.

The post went further;

A GPRS/EDGE phone network can be configured to operate in, commonly, 2 Network Operating Modes (NOM). For Mode 01, if an incoming call occurs during data use the data session will be terminated and the call will come through. In Mode 02, the call will go straight to voicemail, giving the data session preference. Majority of 2G networks in the world use Mode 02!

It is possible to use the iPhone’s field test mode to check what Network Operating Mode a network is using. To do this, first disable 3G, then dial *3001#12345#* from the phone app keypad then pressing call. Go to GSM Cell Environment -> GPRS Information, and scroll down to “Network Operating Mode”.

The ramifications of all this are that any time you use data on GPRS/EDGE you will miss incoming calls and unless you have a missed call service with your provider, you won’t even know you missed them, as they will not show up on the phone.

Not only can this be caused by actively using an app such as safari, (or leaving a data using app active with the screen locked) but background mail checks and push notifications will cause it as well.

I was able to confirm this. The funny thing is, with data switched off, the phone works flawlessly, confirming that the data traffic is the problem. I also carried out the Field Test to confirm the Network Operating Mode of Globacom. Expectedly, it was NOM 2. MTN and Etisalat were also NOM 2.

As far as i can tell, the issue seems to be iPhone (iPad phone) specific as NOM2 seems to work perfectly with Nokia, Samsung and other brands of phones. Worst still, there seem not to be any solution in sight.


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