If you want to be easily reachable from abroad, there is a choice of various DID providers, and some of them offer free service.
SIP Broker is a public service where DID providers share their facilities and use a common database for calling SIP destinations. Unfortunately the original company that started SIP Broker is out of business, and it’s unclear who is maintaining the service now. My emails to their support address remain unanswered for the last couple of weeks. But the service works quite fine.
voip-catalog.com and voip-info.org provide lists of DID providers worldwide, including the free ones.
Zadarma is a Russian VoIP provider, and they offer free DID numbers throughout Russia and also worldwide.
