Why don't you use "to" in this sentence?
Why don't you use "to" in this sentence?
"I recommend you try calling him tomorrow?"

I thought that it should be "I recommend you to try calling him tomorrow".

And, is this correct?
"Tell her to call me tomorrow"
If so, why in this case you have to use "to" but in the previous case you doesn't?

Question

Why don't you use "to" in this sentence?
Why don't you use "to" in this sentence? 
"I recommend you try calling him tomorrow?"

I thought that it should be "I recommend you to try calling him tomorrow".

And, is this correct?
"Tell her to call me tomorrow"
If so, why in this case you have to use "to" but in the previous case you doesn't?

Answer

It's because of the verb "recommend".

"I recommend (that) you try calling him tomorrow."

The fact is, you have to learn these verbs properly as you go. They don't all follow the same pattern.

Answer

"you try calling him tomorrow is an independent clause with it's own subject and verb. Since the verb ("try") has a subject ("you") you would not use the infinitive form ("to try"). If you say that sentence using "that" between the two clauses ("I recommend that you try") it should become more clear. However, "that" is not necessary for your sentence to be correct.

The second sentence is correct because in this case "to try" is in the infinitive form as it doesn't have a subject.