Thank you for this useful lesson. But if the other person doesn't speak too much, how could I say: "could you please tell him that I called?"

ممكن ان تقول ان اتصلت
or

قوله ان اتصلت

Sorry for the spelling!

Hay Latifa,

Good question! and you were close. to say "Could you please tell him that I called?" You can say:

ممكن تقوله اني اتصلت؟
Mumken taqooluh unny eta9alt?

How about asking the caller: "Can I take a message?".
How is this said in Arabic?

Shokran latifa, shokran Moshaya;
In the street and over the phone, the word (قولّه) or ( تقولّه) is fine because it is not offical conversation (classical),, but gramatically, you should split the word to be (تقول له) but people join them because two (laams) after each other.
Therefore, in classical Arabic, the sentence should be:
ممكن أن تقول له إني اتصلت
By the way,, that can be good example of the difference between colloquial and classical Arabic .

We normally say (ne7keeloh/ne7keelaha shy?) which is (shall we tell him/her something).. This is how we say it in Arabic, where something is refering to the message.
Hope that is clear.