"Dost number on" is an informal way of saying "friend, are you there?" or "friend, can you hear me?" There are many synonyms for this expression, such as "hello friend," "hey there buddy," "what's up pal," "yo mate," "how's it going chum," "hiya matey," "hey amigo," and "what's new bud?" These expressions are used to initiate a conversation with a friend or colleague in a casual and friendly manner. They indicate a sense of camaraderie and closeness between the speaker and the listener. Ultimately, the choice of synonym depends on the tone and relationship between the speakers.