  We present detailed calculations about the expected shape of two-pion
Bose-Einstein (or HBT) correlations in high energy heavy ion collisions that
include a realistic treatment of final state Coulomb interaction as well as
strong interactions (dominated by s-wave scattering). We assume L\'evy type
source functions, a generalization that goes beyond the Gaussian approximation.
Various recent experimental results found the use of such source types
necessary to properly describe the shape of the measured correlation functions.
We find that strong final state interactions may play an important role in the
shape of the two-pion correlation functions, especially if one considers source
parameters beyond the Gaussian HBT radii. Precise experimental determination of
these source parameters (such as L\'evy stability exponent, correlation
strength, etc.) seems to require the inclusion of the treatment of strong
interaction not just for heavier particles (e.g. protons, lambdas) but also in
case of two-pion measurements.
