Given the mobile phone's high market penetration and strong upgrade rate, it suggests itself as a natural candidate to support, and eventually host a user's digital representative. Coupled with artificial intelligence techniques, a phone-borne digital representative takes the form of a mobile assistant. Mobile assistants can circumvent hardware constraints (CPU cycles, narrow or expensive bandwidth, small memory, and limited user interface). They can also enable a set of new services that draw on the user's personal preferences, the user's location, available services, and the mobile phone's support of short-range connectivity. Although mutually independent, both capabilities, taken together, yield a powerful, digital representation of the mobile user. This digital representation can provide an optimal user experience, i.e., maximal connection to relevant services, without information overload or expensive wireless service charges. The article addresses three topics: the emergent mobile computing environment; the characteristics of mobile assistants that enable them to operate in this environment; and proposed mobile assistant architectures which target both current and future mobile phones.