The original Ramji Rao Speaking has a sequel called Mannar Mathai Speaking (1995), which was also a critical and commercial success and inspired a remake (Bhagam Bhag).

But I've just found out that there's yet another sequel, Mannar Mathai Speaking 2 (2014) and:

The film received negative reviews from critics. Sify movies commented, "You can only watch Director Mamas's Mannar Mathai Speaking 2 with tremendous anger and disbelief as he makes a mockery of two much loved films with this one. Please don't speak again, Mr. Mannar Mathai!" Rediff movie reviews commented, "Mannar Mathai Speaking 2 is a repeat of what we've seen before."

... Yikes.

Let's hope history doesn't repeat itself with the Phir Hera Pheri sequel.