1) I wouldn't use it in writing such as in essays, because it's normally used when you're speaking to someone in particular. You can use it while, for example, writing a letter, an email or a text to a friend. Otherwise, if you have to write a formal letter, you'd want to use "Mi dica", instead. 2) "Dimmi" and "Diceva tu" don't mean the same thing, and, actually, "Diceva tu" is not even something you would here in Italy, first cause the verbal conjugation is wrong, second because we put the pronoun first and then the verb, so it would be "Tu dicevi"; said so, "dimmi" is present tense of the imperative form ("tell me"), while "tu dicevi" is past tense of the indicative form, and i think the closest way to translate it is either "you were saying" or "you used to say". So, yeah, there are some differences. 3) No, this form doesn't exist in italian.

About /telefonami/ (tu form): 1. Telefonami piu` tardi. 2. mi telefoni piu` tardi? (only as a request, with interrogative tone) (lei form): 2. per favore, mi {+potrebbe, puo`} telefonare piu` tardi? 3. mi telefoni piu` tardi. Note that the form (3) might be used only when the speaker has clearly the power of giving order to the listener, so it is not a kind form, it is the true imperative (= command) form. Form (2) is perfectly kind (una forma gentile).

Imperative form (present): a) tu dici a me (never abbreviated) Indicative form (present) b) Tu di` a me (almost alway abbreviated in: [tu] dimmi) The imperative form needs the listener to be present, so it is rare in written text, and is used mainly in two contexts: c1) when giving orders (the etimological root is the same of 'empire') c2) when talking to a friend or in a friendly way to somebody. For instance, if you are visiting a place with a friend and you see something interesting you would say to your friend: (examples) e1) [--tu] guarda la`, che bel palazzo (building) ! Here /guarda/ is 'present imperative' (answering a phone call) e2) scusami, ma adesso ho molta fretta (I'm quite in a hurry), telefonami piu` tardi (later) per favore. Here /telefonami/ has exactly the same construction as /dimmi/, just with a single 'm'. (to pupils at lesson, this is both (c1) and (c2) as usually teachers have good feelings towards students) e3) ascoltate bene, perche` questo argomento e` di base per tutto il nostro corso. ===== /dicevami/ and similar forms are rarely used anymore, some survived, but usually in the present tenses. A use of dicevami is when words that have been said must be reported as they are, as in: -- "vedo una lontana terra", dicevami il marinaio, "finalmente avremo dell'acqua e del cibo", ma io temevo di trovare il nemico su quell'isola e ordinai, anche se con il cuore in pezzi (even if with a broken heart), di non avvicinarsi e di tenere il mare alto (to stay away from the shore). In this case /dicevami/, being a single word makes a shorter break in the words of the sailor, but are the key of the whole meaning. Anyway a typical Italian, like me, could go along all of its life without ever saying /dicevami/.

/ce le spieghi adesso/ goes like this: a noi loro spieghi adesso (this form is NOT used) ce == a noi le == loro (direct object, plural, feminine, related to 'domande') Usually /a noi/ is /ci/, but it MUST turn to /ce/ in contexts as: /ce ne/, /ce le/, ... The correct usage of (ci,ce,le,ne,...) is not easy and would come after a lot of practise, be assured that, although Italians know it, it is NOT EASY for them (and also for me) to correctly recognize the proper grammatical role of each of these concise and with multiple meanings function words.

Sorry, you are right (it was late in the night when I wrote the last answer), actually the following is true: (lei relation) lei telefoni : present imperative, third single person. Indicativo presente io telefono tu telefoni egli telefona noi telefoniamo voi telefonate essi telefonano Imperativo presente (the pronoun is used very seldom) (Io) (missing verbal voice) (tu) telefona (egli, lei, ...) telefoni (noi) telefoniamo (voi) telefonate (essi, loro) telefonino