  A generalized Baumslag-Solitar group is the fundamental group of a graph of
groups all of whose vertex and edge groups are infinite cyclic. Levitt proves
that any generalized Baumslag-Solitar group has property R-infinity, that is,
any automorphism has an infinite number of twisted conjugacy classes. We show
that any group quasi-isometric to a generalized Baumslag-Solitar group also has
property R-infinity. This extends work of the authors proving that any group
quasi-isometric to a solvable Baumslag-Solitar BS(1,n) group has property
R-infinity, and relies on the classification of generalized Baumslag-Solitar
groups given by Whyte.
