Alison DiLaurentis had four phones through this show. She used her phone, to keep in touch with Ezra Fitz, Ian Thomas, and her friends and family, use the internet and receive A's Messages. Currently, she has an iPhone 4S.
In the second season Halloween episode, "The First Secret," or earlier, after Alison meets Jenna in Halloween costume shop, she receives a message from "A" on her pink, Motorola V3i cell phone.
A year later, in Pilot, "A is for Answers," after she threatens to Jenna stop threating her, Alison receives a messages from "A" on her iPhone 3GS with a black case.
Later in "EscApe From New York," she uses a burner phone in New York which she bought from a convenience store
In "Thrown From The Ride" you see Alison texting Emily with a white iPhone 4S in a white case.
In Hush Hush Sweet Liars, Alison has a gold iPhone 6 Plus with a case similar to Spencer's iPhone 5 case but pink