You can use VoIP with every internet connection (DSL, Cable, UMTS, LTE etc.) worldwide if the up-/downstream is at least 80 kbps.
You can call with any telephone if it’s connected to a VoIP compatible router (eg. FRITZ!Box or Speedport). You can also call via a smartphone app, a softphone via PC or an IP phone.
You will also get a real local phone number, so you’ll be available from any phone worldwide with this number.