Understanding the Network list and how to tell what network you're on

One of the most common questions is "When I use 'Select Network' I see two or more networks, and they all say 'Cingular'.  How do I know what these networks are?

Cingular has been built over the year merging smaller wireless carriers in to one large carrier.  The most best known merger was between AT&T Wireless and Cingular.  Once these mergers occur, customer gain the ability to use the networks from both of the former companies.  In addition to that there are other GSM carriers out there, some of which Cingular lets you roam on when a Cingular tower is not in range.

Around 2003-2004 the wireless companies did away with roaming charges to promote national plans.  In some areas where Cingular doesn't have good coverage, they allow you to roam on a competitors network, free of charge to you.

As a result at any given time you may be using any one of Cingular's networks or be roaming on a competitor.  Since all of this is free of charge and included in your national plan, they want to give you the illusion that you're simply using 1 network because quite frankly it should seamless to you.  As a result they override the alpha tags broadcast by the GSM towers and always show "Cingular" as the carrier name rather than show "T-Mobile", "Edge Wireless", "AT&T Wireless," etc.  This prevents customer confusion and phone calls of worried customers thinking they're getting charged roaming or not on a Cingular network.

I will point out that when you're outside of the US, this alpha tagging override does not take place,  They allow you to see the network name you're actually on.

By now Cingular has actually consolidated most of their networks so that they truly are one seamless network, and they've ended roaming agreements with competitors in most areas.  But there are some places like California where there the coverage is supplemented by T-Mobile or entire areas are supplied by another carrier.  This is one of those cases where it's beneficial to be able to manually switch between the two networks, either of which you are fully allowed to use.

When you chose "Select Network," you'll see every every GSM network in range, regardless of weather or not you're allowed to use it.  Although you can't tell, the screen shot below shows two networks which are "310-380 Cingular (formerly AT&T)" and "310-170 T-Mobile (formerly Cingular.)"  Cingular sold their network to T-Mobile in this case and has contracted to keep their customers covered by it until 2007.

Your SIM contains a preferred network list.  This list is all networks that your phone is allowed to automatically use or roam on to.  The first entry is your home network, and your phone will always try to register with a network that is highest in the list.  This is another advantage of manual network selection.  If you see a network that is not in your SIM's preferred network list and it is one you're actually going to be allowed to use, you can manually register with that network.  Since it's not in the preferred network list, your phone would never automatically roam to it even if you had no other signal.  This situation, however, is very rare and if it does you should probably call Cingular and ask them to update your SIM's proffered network list so you can roam on the carriers in that area.  But without the manual network selection hack, you might never have known there was a network there you could use.

In my case my SIM's home network is Cingular 310-410.  In most of California we actually have the networks 310-380 (Cingular/formerly AT&T) and 310-170 (T-Mobile/Formerly Cingular.)  Since 310-170 used to be the primary Cingular network, the preference order in my SIM is:
310-410
310-170
310-380
(there are others that I have not listed)

In areas or other states where 310-410 is the network, my phone will happily use it.  In California, however it's forced to use another network in the list, 310-170.  If 310-170 is not available, it'll try to use 310-380.
In the below screen shot, although you can't tell from this screen, you're seeing the 310-170 highlighted as being currently in use.  And below it is network 310-380, which is the only other network in range and is second in my preferred network list.  As far as I can tell what you see on this list is always in the same order as your SIM's preferred network list.  And if it's not in the list they will show up at the bottom of the list.

How to actually tell what network you're on

So how do you know which network is which?  Well the short answer is you don't.  You can try each network, and if it works, there is a way to tell what network you're on.  But if you're denied the ability to register with the network then there (so far) is no way to know what the network number is.

The Treo has a file called CurrentCarrier.pdb.  I haven't been able to determine it's purpose, but it does show you the network that you're currently registered with and using.  Also the text contained in these records is what shows up on the phone application as the network name.  So if you edit the text in this file it'll be reflected in the phone app.

There are two records in CurrnetCarrier.pdb:
Record 0: Is your home network.  It's the first network in your SIM's preferred network list.  Record 0 never changes unless you change SIMs and doesn't show you the status of anything except what network it will consider your home and primary network.
Record 1: Is the the current network you're registered with and using.  So if you use "Select Network" to change to another network.  Open up CurrentCarrier.pdb and look at record 1 to see what network you're actually on.

If you use the program FileZ, you can look at the CurrentCarrier.pdb to see which network you're actually registered with at the moment.

1) Open up the program FileZ, select 'View and Edit files," and expand "Internal."

2) Find the file "CurrentCarrier.pdb" and select it by placing a check mark next to it.

3) Select "Menu", "Item" and "Edit."

4) Select "Record 0" then "View"

This is what the phone considers your "Home Network."  It's comes from the first entry in the SIM preferred network list, is considered your home network, and is the network your phone will always prefer to be on.

5) Press Close, then select "Record 1" then "View."

This is the network that you are your phone is currently registered and using.  What you see in this record will change when you switch between networks.  In most cases it's the same as what's in record 0 but in cases where you're using a network other than your home/preferred, it will be different as in this case.

Finally, you can edit the text portion of these records (using edit instead of view) and actually change the text output on the phone application screen.  However this change won't remain permanent.  As soon as your phone re-registers due to roaming, loss of signal, or phone on/off, this is overwritten with the Cingular again.