The realization of scalable quantum networks for distribution of entanglement over long distances hinges on quantum repeaters. To outperform the exponential transmission loss in optical fibers, quantum repeaters must employ multiplexing schemes in the temporal, spectral, or spatial domain. The performance of such a multiplexed scheme is contingent on efficient quantum memories offering both extended storage times and large multimode capacities. Towards this goal, we experimentally demonstrate a memory platform operating at telecom wavelength using an Er:YSiO crystal. We record on-demand storage and recall of weak coherent pulses for up to $1$,ms, exceeding by an order of magnitude that of previously reported demonstrations based on Er. The memory exhibits an efficiency of 10.36% at 300,$\mu$s storage time with a signal-to-noise ratio of $10.9$, mainly limited by spontaneous emission noise. We also store two spectral modes representing a frequency-bin encoding and retrieve the state with an overlap of 81.8%. Furthermore, we demonstrate multimode capacity by simultaneously storing 20 temporal and 3 spectral modes with on-demand and selective recall capabilities, serving as a promising step toward a scalable quantum repeater architecture.