Sure, you'll get more juice from a single charge out of the 3125 than the i-mate Smartflip, Qtek 8500, and Dopod s300, all based on the Star Trek, but you also get a thicker and heavier smartphone in the process. It leaves a little hump in the back of the 3125 as well (see image below from engadget).

Cingular could have chosen to make the higher-capacity 1100 mAH battery optional, saving consumers a little extra bulk and weight, but that would have almost certainly meant the carrier would have sacrificed what consumers saw as the standard talk (4 hours) and standby (6 hours) time by default.

Plus, it probably wouldn't have impacted the already reasonable price, $149 with the standard two-year service contract, and you would have had to pay more just to get the more powerful battery if that ended up being what you wanted in the first place.

More on Cingular 3125
The quad-band (850/900/1800/1900 MHz) GSM/GPRS 3125 comes in two flavors, one with a 1.3 megapixel camera for picture and video and the other, called the 3100, without a camera. Otherwise, both versions appear to be the same, measuring a compact 3.88 x 2.02 x 0.64 inches and weighing only 3.49 ounces.

There's also a 200 MHz TI OMAP 850 processor, Bluetooth 1.2, microSD slot, 64 MB of RAM, 128 of ROM, a 2.2-inch 240 x 320 (QVGA) pixel resolution display, and a second external color display.

As a Windows Mobile 5.0 for Smartphone device, the screen isn't touch.

Cingular is loading Microsoft's Messaging and Security Feature Pack to provide users with push e-mail and data access (including calendar, tasks and contacts) and more for Exchange server out of the box. Additional mobile e-mail arrives with support for Good Mobile Messaging from Good Technology and SEVEN-run Cingular Xpress Mail, which is compatible with many popular Internet Service Provider services.

To play MP3s there’s Windows Media Player 10 Mobile. The 3125 also has a speakerphone and EDGE network support, a 2.5 G technology that exchanges data at about 70 to 135 kbps.