It is indeed the latest trend in the film industry for top actors to do guest appearances.
Though it's very common in Bollywood, in Telugu, not many actors were game to appearing in films where they did not play the lead.
But times are changing and so are the Telugu actors. It is no longer considered to be bad to put in a friendly appearance.
Joining the bandwagon or rather setting a trend is young actor NTR. News is that he has done a couple of scenes for Visakha Express which has Allari Naresh in the lead.
In case you wondered, why he would do that, the film is presented by SS Rajamouli. Now, doesn't that explain a lot?