Apple moved away from the 4-inch form factor in 2014, settling with the 4.7-inch and 5.5-inch sizes. The two new sizes fit with the high-end Android range, from smartphone to phablet.
Next year, we may see a return to the 4-inch iPhone, according to various supply chain sources. The return of the 4-inch size may be due to the removal of the iPhone 5C and iPhone 5S, the two last 4-inch devices on Apple Stores.
Even though the market has shown interest in the larger devices, the continuation of sales from the iPhone 5C and iPhone 5S may have spurred Cupertino to create a new device in 2015, with the same form factor as previous iPhones.
The 4-inch iPhone will most likely be the lowest end of the five reported devices coming in 2015. Other reports say the iPhone 6S will launch in Summer and the iPhone 7 will launch in Winter of 2015 — a big change from the norm.
As tradition now, the iPhone 6S and iPhone 7 will most likely come with a larger model, the Plus. It is unclear if Apple will stick to a yearly announcement for the Plus, which would lower the amount of devices launched this year to four.
Apple has always had issues when it comes to supply, due to the overwhelming demand for one device. The only company to match Apple — when it comes to individual device sales — is Xiaomi in China.
The 4-inch iPhone would perk up users who are still unsure on the larger device size and see the iPhone 6 as too large of an upgrade. Not many providers offer high-end phones with such a small display — it would provide customers who want the high-end performance but do not want the large screen.