How to make domestic calls in a foreign country without an international plan

Receiving calls and getting text messages with a registered number is necessary all the time nowadays. For example, many two-step log-in sends a code to a phone number. This means one needs his domestic phone number active on a phone even when he travels internationally. The easiest, but often costly, way is buying an internal plan.  

There is a good alternative:

It is a good idea for someone to have two phones for an international trip just in case a phone is out of order. Suppose one usually uses his phone A with a domestic SIM card and a domestic phone number registered in many places. When he travels, he brings an additional phone B as a backup. B can be an old retired phone. 

1. When one is at a place with free Wi-Fi, he can call with A via Wi-Fi calling just as he does at home. In other words, the it is equivalent to being physically at home to make calls.
2. When there is no free Wi-Fi available, he needs phone B to setup a Wi-Fi hotspot.
   1. Buy a SIM card with adequate data (10GB should be enough for a 2-week trip). It costs about $5 in Ukraine, maybe $20 in Poland.
   2. Activate this SIM card in phone B. You can use phone B to make local calls.
   3. Turn on the Wi-Fi hotspot of phone B.
   4. Connect phone A to phone B's Wi-Fi spot to get internet access,  text and calls for the domestic phone number.
   5. If you use a laptop, you can connect it to phone B to get it online when there is no free Wi-Fi.