We communicate with our friends, teachers, …

First of all this is a great question! We communicate with our friends family or any other human being through physical ways such as letters emails etc or through talking verbally because we see them. We can observe them we know their presence but God is not there in front of us therefore we communicate with him mentally. Also this is an age old saying that "God knows everything" therfore we are certain that whatever we will try to convey to him he will know it without wanting us to say it. We cannot communicate with humans mentally because they are incapable of such an act but God has that capability as we read it in our holy books. Lenchos condition and the condition of PK is very similar because PK also in the beginning trusts God that he will help him to get his remote back and that God helps everyone so he will help him too because of which he goes to every temple,mosque,church,gurudwara etc. In the hope to get help from God and in the end god makes him meet anushka Sharma who helps her fight against the authority to win his remote back. The same situation is with lencho too he believes in God that after his crops failed God is the only one to help him and he was so certain that God will help him in that hope he writes a letter to God. And God makes him meet a kind post master who helps collect donation and gives the money to lencho to help him.