Hello Estella, "tramite" and not "attraverso" means 'per mezzo di'( by means of ). The main difference in meaning between both is as follows: tramite: means "by means of", which means using any mean as a method of transfer in the context of your examples. It also means "through" ,but concerning persons ,through someone. So in your example Nr 2 ,it would be more convenient to use " tramite lui"," tramite una persona (lui)". attraverso : means "through" or "across". In Nr 1 ,the message could be transferred through the radio or by means of the radio. Both apply with difference in meaning. Using 'attraverso' the radio, means the message is transferred through the radio. It refers to the technical process of transfer,while using 'tramito" here means by means of , through the radio as the tool or method of transfer in this case. I assume in Nr3 you mean by "posto" "posta" which is mail . Here you can use "tramite" posta ,in the sense of 'by means of' or 'per': perché non lo mandi per posta? Why don't you send it by post? 'per' is used more often in this context. I don't think that "attraverso posta" is appropriate here. A radio transmission happens through a media ,so you use "attraverso",while the mail transfer happens through vehicles .So you better use "tramite" or "per" here.

Ciao, non sono un letterato per cui ti rispondo secondo l'italiano corrente. Secondo me i due termini sono intercambiabili relativamente alla "radio"(tramite la radio, tramite radio, attraverso la radio) Nel caso di "lui" credo sia piu' comune "tramite lui" rispetto ad "attraverso lui" ma sono corrette ambedue le forme. Rguardo il termine"posto" non si capisce il contesto. Ci vorrebbe un esempio di frase piu' completa.