The 25 series MOS is for the Army Signal Corps. Here are some of the MOSs in the 25 series:
Information Technology Specialist (MOS 25B)
Electromagnetic Spectrum Manager (MOS 25E)
Network Switching Systems Operator-Maintainer (MOS 25F)
Cable Systems Installer-Maintainer (MOS 25L)
Nodal Network Systems Operator-Maintainer (MOS 25N)
Microwave Systems Operator-Maintainer (MOS 25P)
The 25U MOS is for Army Support Operations Specialists. These specialists work with battlefield signal support systems and terminal devices. They integrate signal systems and networks, perform maintenance on signal equipment, and provide technical assistance to users. They also configure and troubleshoot local area networks and routers.
The 25S MOS is for Satellite Communications Systems Operator-Maintainers. These specialists supervise, install, operate, and maintain satellite communications ground terminals, systems, networks, and associated equipment.