  We derive constraints on a simple quintessential inflation model, based on a
spontaneously broken Phi^4 theory, imposed by the Wilkinson Microwave
Anisotropy Probe three-year data (WMAP3) and by galaxy clustering results from
the Sloan Digital Sky Survey(SDSS). We find that the scale of symmetry breaking
must be larger than about 3 Planck masses in order for inflation to generate
acceptable values of the scalar spectral index and of the tensor-to-scalar
ratio. We also show that the resulting quintessence equation-of-state can
evolve rapidly at recent times and hence can potentially be distinguished from
a simple cosmological constant in this parameter regime.
