I myself used to use the Zadarma service very actively, choosing it for convenience and tariffs among similar Internet telephony providers. As a rule, all contact phones on sites, including mine, are virtual SIP numbers. They cost a couple of dollars a month, and in case of a call to them, the call is forwarded to a working phone. To make a call from such a number yourself, you need to install one of several applications for SIP telephony on your smartphone and configure it for your operator. But recently, Zadarma developers have made their own dialer application, thus greatly simplifying communication. In fact, this is the same Viber or Skype only with a real phone number … 
To start using the application, you first need to register on the zadarma.com service website. Select the desired tariff and, if necessary, the phone number for incoming calls. You can make calls to other subscribers without your own number, just in this case, the general service number will be displayed in the incoming ones. For all kinds of calls, this is even good 🙂 After that, in the “Settings” – “SIP settings” section, you need to set a password for the application and remember your digital login. 
Now you can install the application itself on the iphone and use your digital login and the specified password to enter the program. 
It differs from similar universal applications in that all communication settings there are already preset for a specific Zadarma service. The program imports phone books and the entire contact list can be used as in a native dialer iPhone. 
Internet connection is good enough, 3G allows you to communicate without feeling any digital artifacts. Even signal latency is not much different from cellular. 
Of the minuses, I can only note the impossibility of sending and receiving SMS, but in the Russian part of IP telephony, no one has such a service. Therefore, for those who often call mobile or landline numbers abroad, I recommend trying this application. Well, the owners of the Internet business have probably already appreciated the possibility of Internet telephony for a long time, placing virtual numbers on their sites.
