The evaluation and comparison of the optical properties in the O and C bands of silicon nitride rib waveguides with integrated Ge_2Sb_2Te_5 phase-change cells is reported. In straight rib waveguides, a high transmission contrast is observed in both bands when the Ge_2Sb_2Te_5 cell is switched between states, being up to 2.5 dB/μm in the C-band and 6.4 dB/μm in the O-band. In the case of silicon nitride ring resonator waveguides, high quality factor resonances (Q ∼ 10^5) are found in both bands, leading to the provision of an ON-OFF switch characterized by an extinction ratio of 12 and 18 dB in O and C bands respectively. Finally, with the view to provide a comparison of the wavelength-dependent optical switching of the phase-change cell, a 3-dimensional finite-element method simulation is performed and a comparison of the optical-to-thermal energy conversion in both bands given.