  It is well-known that $f(R)$ theories are dynamically equivalent to a
particular class of scalar-tensor theories. In analogy to the $f(R)$ extension
of the Einstein-Hilbert action of general relativity, $f(T)$ theories are
generalizations of the action of teleparallel gravity. The field equations are
always second order, remarkably simpler than $f(R)$ theories. It is interesting
to investigate whether $f(T)$ theories have the similar conformal features
possessed in $f(R)$ theories. It is shown, however, that $f(T)$ theories are
not dynamically equivalent to teleparallel action plus a scalar field via
conformal transformation, there appears an additional scalar-torsion coupling
term. We discuss briefly what constraint of this coupling term may be put on
$f(T)$ theories from observations of the solar system.
