f()
{
    IFS=:
    for arg in $1
    do
        echo arg: $arg
    done
}

f foo:bar:baz

$ dash foo.sh
arg: foo
arg: bar
arg: baz
$ bash foo.sh
arg: foo
arg: bar
arg: baz
$ ksh foo.sh
arg: foo
arg: bar
arg: baz
$ posh foo.sh
arg: foo
arg: bar
arg: baz
$ yash foo.sh
arg: foo
arg: bar
arg: baz

$ zsh foo.sh
arg: foo:bar:baz