We introduce phase-change material Ge₂Sb₂Te₅ (GST) into metal–insulator–metal (MIM) waveguide systems to realize chipscale plasmonic modulators and switches in the telecommunication band. Benefitting from the high contrast of optical properties between amorphous and crystalline GST, the three proposed structures can act as reconfigurable and nonvolatile modulators and switches with excellent modulation depth 14 dB and fast response time in subnanosecond while possessing small footprints, simple frameworks, and easy fabrication. We provide solutions to design active devices in MIM waveguide systems and can find potential applications in more compact all-optical circuits for information processing and storage.