User equipment to transmit signals (e.g., concurrently) using multiple SIMs. If the user equipment determines to perform transmission power back-off due to operating using the multiple SIMs (MuSIM operation), the user equipment sends an indication to each network corresponding to each SIM that it is performing the power back-off. If a network supports MuSIM operation, then the user equipment sends an indication that it is performing the power back-off due to MuSIM operation (e.g., an MuSIM Maximum Power Reduction (M-MPR) indication). For such a network, it is assumed that the M-MPR indication would be standardized under an applicable specification. If a network does not support MuSIM operation (e.g., a legacy network), then the user equipment leverages a legacy power back-off indication (e.g., a Power Management Maximum Power Reduction (P-MPR) indication) to indicate to the network that it is performing a power back-off.