  Internet of Things (IoT) and B3G/4G communication are promoting the pervasive
mobile services with its advanced features. However, security problems are also
baffled the development. This paper proposes a trust model to protect the
user's security. The billing or trust operator works as an agent to provide a
trust authentication for all the service providers. The services are classified
by sensitive value calculation. With the value, the user's trustiness for
corresponding service can be obtained. For decision, three trust regions are
divided, which is referred to three ranks: high, medium and low. The trust
region tells the customer, with his calculated trust value, which rank he has
got and which authentication methods should be used for access. Authentication
history and penalty are also involved with reasons.
