Effe is probably used about as common as gonna is in English. I really don't think it should be deleted.
I find the analogy not perfect. Gonna has a difference in pronounciation compared to "going to", has a different background (is an enclise, not a spelling variant), and is recognized in written language in a way that surpasses chat and sms language (i.e. used in films, songs and books). And why, for you, does "effe" warrant an entry and other -en words which have n-deletion do not? What's the criterion of inclusion? Morgengave (talk) 09:54, 19 January 2013 (UTC)
I don't understand why you say that effe is used only in chat and sms language. There are many hits of the word on Google books. As for the criteria: if it is attested according to WT:CFI, it can be included. So that includes forms without -n and other colloquial respellings.