This method does not give you the full 11 maps. Instead, it gives you San Andreas PLUS Vice City, or San Andreas PLUS Liberty City.
While the mod originated on PC, its migration to Android has brought the "all-in-one" experience to mobile devices. GTA: Underground - Combining the 3d era gta underground mod android
This involves taking the PC map files and converting them using and "IMG Tool." You will spend 10+ hours on this. This method does not give you the full 11 maps
that aimed to merge several Rockstar Games maps—including , Vice City , Bullworth (from Bully ), and Carcer City (from Manhunt )—into a single, seamless world. Status and Availability Bullworth (from Bully )