Programmable gestures, like those used with graphics pads and on computers, have been around for ages, but it's a bit of a rarity in the cellphone world. In fact the full-face touchscreen as a viable cellphone controller interface, thanks to the success of the iPhone, has only recently been accepted by the mobile phone community.
Samsung's technology is about more than just fixed single- or multi-fingered gestures drawn on a touchscreen though. The phone can recognize a variety of gestures--each a letter of the alphabet--to unlock it. Given that it's highly unlikely that you'd accidentally draw a letter "A" on the Samsung devices; as a security feature, it's not bad at all. But the real trick is that you can select which application will launch immediately after the unlock for each letter: you want to go straight into the SMS menu, so you might draw an "S" or a "P" for phone calls, since it's user-selectable.
It's a subtle development for a touchscreen UI, but it's probably quite a handy one. The two phones that will carry the tech are, however, pretty low tech in many other ways. Unlike the iPhone or the G1, both are mid-range devices. The S5600 is a 3G unit with a 2.8-inch 240 x 320-pixel touchscreen, a 3-megapixel camera with smile detection and 7.2mbps HSPA connectivity. The (presumably) cheaper S5230 features a very similar design, at least on the outside, but lacks 3G connectivity and has a 3-inch screen with 240 x 400 pixels. Both are quad-band phones that run Samsung's TouchWiz UI, as well, they have microSDHC memory expansion, in-built FM radios, and Bluetooth. They'll debut in Europe first starting in April.
It would be interesting if the current king of touchscreen interface design took a leaf from Samsung's book with its upcoming rumored iPhone version 3.