IE Cingular Proxy Registry Hack for the Treo 750
For PalmOS Treo 750 Cingular Branded Treo 750.
This may not apply to non-Cingular branded Treo 750.

Download these two .cab installer files:
Download: DisableCingularProxy.cab
Downlaod: RestoreCingularProxy.cab

To Install: Download and install DisableCingularProxy.cab.  (Modifies 1 registry value)
To Uninstall: Download and install RestoreCingularProxy.cab (returns registry value to default)
I recommend you download both them to the My Device/My Documents folder.  Then just install each one at will to toggle between enabling and disabling the proxy setting.

What does this .CAB installer do?
These .cab installers make 1 change to the windows mobile registry as described here.  It does not install any files or other hacks, just makes a registry change:

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings]
The default setting (that uses the proxy) and the setting 'RestoreCingularProxy.cab' sets the value to is:
"EnableAutoDetect"=dword:00000000

The DisableCingularProxy.cab file changes it to:
"EnableAutoDetect"=dword:00000001

If you prefer to use .reg files to import the above described changes directly using a registry editor such as Resco Explorer registry editor add-on rather than using the .cab files (which don't require a reg editor,) then here are the .reg files for importing.
DisableCingularProxy.reg
EnableCingularProxy.reg

What is this:
In the simplest of terms, Pocket Internet Explorer (the web browser) on the Cingular Treo 750 is configured to use the Cingular proxy "wireless.cingular.com."  This appears to be done for the purpose of allowing you to browse to Cingulars MEdia Net home portal at the URL: http://device.home/.  This is a WAP site and can not be accessed by a normal web browser without going through the WAP proxy server (wireless.cingular.com.)  A typical cel phone with a WAP browser (like any ordinary flip phone) doesn't need special configuration because it connects through the WAP gateway by default.  But PDAs are designed to access the internet directly.

The problem with this is that there is no way through menus or configurations to disable or change this setting.  This hack (or registry edit) will disable this setting (as well as re-enable it.)

What are the ramifications of this proxy setting:
The Pros:
1) Some image compression resulting in smaller faster image (images in a web page for example) downloads with lower quality graphics.
2) Ability to access the MEdia Net web site at http://device.home/ and partake in it's services, including Cingular Video.  Instructions for making Cingular Video work on the Treo 750 can be found on this site.

The Cons:
1) Inability to use Pocket Internet Explorer with a MiniSD WiFi network card (eg. Spectect MiniSD Wifi Card)
2) Inability to use Pocket Internet Explorer with the 'Data Connect' Access Point called "isp.cingular" (included in the PDA connect plan)  The wireless.cingular.com proxy is ONLY available through the wap.cingular access point.
3) Sluggish internet browsing response due to the proxy.   This is increased latency because of the proxy as a middle man even though.  Even though it compresses images to reduce data download (to speed it up) the result is overall slower web browsing
4) Degraded image quality.

Who Needs this, do I need this?

In most cases, for most people, you may not want to use this.

You do not need to disable the proxy.  Most people will find the default configuration (with proxy) completely acceptable and convenient.  Disabling the proxy limits your ability to access the Media Net home page (http://device.home/ ) as well as Cingular Video (not supported on Treo 750 without a hack, available here.)

The intent of setting the proxy this way is so that IE can access the proxy server without configuring the Treo's network connection to send all of the device's data through the proxy.  Your email applications and all other apps on your Treo will NOT use the proxy, only IE will because this proxy setting tells it to "Auto Configure to use the proxy" for web browsing.

You only need to do this registry hack if:

1. You are are trying to use the isp.cingular access point connection.  IE will not be able to acces the proxy server through isp.cingular.

2. You are trying to use a MiniSD WiFi Card (like the Spected MiniSD WiFi Card.  IE will not be able to acces the proxy server through WiFi.

3. You are trying to increase 3G speeds.  The proxy server could act as a bottle neck for 3G data as well as increase latency in download response.

Technical Jargon:
Access Points:  There are two access points you can use to connect to the internet.  wap.cingular and isp.cingular.
Wap.cingular is the "Media net" access point and is the default connection for all phones and PDAs.
Isp.cingular is the "Data Connect" access point and is the standard connection for laptop internet cards and Laptop 'tethering' (use phone as a modem.)
Proxy: The proxy address is wireless.cingular.com.  This proxy allows you to access http://device.hom/ (or http://home/ ) which is the Cingular Media net WAP site.

Finally to the point.  What is the registry edit?
This is not a hack, it's a very simple registry change.  It is documented by Micorosft MSDN and is a supported carrier feature at http://msdn2.microsoft.com/en-us/library/aa457989.aspx (search the page for 'EnableAutoDetect')

Download these and "save as" to your "My Documents" folder.  Then just click and install them to enable or disable the proxy at will.

To verify that you've installed it, attempt to browse to http://device.home/ .  If you can reach the site, the proxy is enabled.  If you can not it (should be) disabled.  Of course if you try to use the isp.cingular access point or a MiniSD WiFi card, you will not be able to browse the internet if the proxy is enabled, and you will be able to if it's disbaled.

More detail on this registry setting can be found at my original post on Howard Forums
http://www.howardforums.com/showthread.php?p=8555248