It looks to support all distribution in the R stats
package: http://stat.ethz.ch/R-manual/R-patched/library/stats/html/Distributions.html since the functions in the truncdist
package prepend "d" and "p" for calls:
g <- get(paste("d", spec, sep = ""), mode = "function")
G <- get(paste("p", spec, sep = ""), mode = "function")
and their paper doesn't specify any restrictions.