Average owner will spend around $56.18 per device.
New data from researcher ABI says smartphones will account for $20 billion in accessory revenues in 2012, more than half of the $36 billion generated across all mobile handsets.
And the smartphone market is only expected to continue growing too, with accessory revs reaching $38 billion within the next five years.
Meanwhile, feature phone accessory revs are set to fall to $12 billion, a market which was once captained by Nokia third-parties several years ago, powered by psychedelic removable fascias.
The average smartphone owner will shell out around $56.18 per device on extras, with feature phone users spending half that at around $28.17 per device.
Michael Morgan, senior analyst for devices, applications & content, ABI Research, said: "The increasing penetration of smartphones is driving a shift in accessory design toward smart accessories that drive higher levels of consumer interaction, product value, and brand recognition.
"For new market entrants, developing brand recognition is paramount in capturing market share from the incumbents. This is best accomplished by the development of engaging, innovative accessories that extend the value proposition of today's mass market accessories."