This option allows the specification of a much broader set of numbers
that tel: URIs, which are limited to global phone numbers in
international form and prohibit local numbers and other useful strings
like "*100#".

This functionality is implemented as a command-line option rather than
a "dial:" or "callto:" URI scheme for the same reason given in RFC
3966, section 7.3:

  '"Callto" was discarded because URI schemes locate a resource and do
  not specify an action to be taken.'