Nearly 50 companies helped define the Mobile Trusted Module spec, which was posted and made available for free at the Web site of the Trusted Computing Group, a largely PC-focused technology standards body. However, two of the largest cell phone chipmakers--Qualcomm and Texas Instruments--didn't participate in developing the spec. Indeed, the only carriers involved were from Europe: France Telecom and Vodafone.
To work for the many different parties in the cell phone market, the MTM spec allows both local and remote roots of trust. A root of trust is a key or certificate typically expressed as a number that can be obtained only by a calculation using information private to a system or user. Local roots of trust can support multiple users of a single handset. Remote roots of trust can allow a carrier, original equipment manufacturer, or application provider to prove it's trusted enough to modify or "reimage" the handset's software.