Oronym — About.com
A sequence of words (for example, "ice cream") that sounds the same as a different sequence of words ("I scream").
The term oronym was coined by Gyles Brandreth in The Joy of Lex (1980).
noun 1. A word or phrase that sounds the same as another word or phrase.
From "Oronyms and Homophones" by Fun With Words,
Oronyms (or homophones) are words which sound the same.
Generally the word homophone is used to describe one of a pair or group of words that have the same sound (like prince and prints; allowed and aloud), whilst oronyms are normally strings of words (phrases) such as iced ink and I stink
Eggcorn — Wikipedia
In linguistics, an eggcorn is an idiosyncratic substitution of a word or phrase for a word or words that sound similar or identical in the speaker's dialect (sometimes called oronyms). The new phrase introduces a meaning that is different from the original, but plausible in the same context, such as "old-timers' disease" for "Alzheimer's disease".
See also: Mondegreen, from a comment by James McLeod