Last month, I posted a teaser video that Israeli startup Modu had put out to get people guessing about what its product might be. The company pulled back the curtains further in advance of the World Mobile Congress in Spain. It turns out that it is a tiny modular phone that can be slipped into different device “jackets”—like an MP3 player, a GPS device, a bigger cell phone, car stereo, or a digital camera. It will launch on October 1 with mobile carriers in Russia, Italy, and Israel. There are no plans for a U.S. launch at this point.

You can think of Modu as an expanded SIM card. It can make a call, send text messages, and hold a contact list—the bare minimum required to be a mobile phone. That is why it is so small—about the size of an iPod Nano. Consumers will be able to carry it around and stick it into different device jackets, depending on the functionality they want. In a camera, for instance, Modu can be used to send pictures over the wireless network. (Although, it will initially only support GPRS, which is slow. Another drawback—there is no WiFi.) The jacket devices should cost less than comparable gadgets with telephony functionality, and the idea is to create an accessory mini-economy around the Modu, so that any device manufacturer could create whatever jackets they like. Modu is the platform, and other companies can build devices around it.

I haven’t seen the device or played with it myself, but the idea of a modular phone is intriguing.

TheMarker provided the video above exclusively for TechCrunch. In it, Modu founder Dov Moran explains the concept. (Thick accent warning).