Imo, /smsmute could be just integrated to /ignore and there you could find an option to disable only player/account SMS or everything.
If will be added in same list, then how we can to know who is ignored or muted only? Then we must to have in same panel, 2 different lines: 1 for ignored players and other one for muted players, right ?
There could be two checkboxes (once you select the player from your list) if you want to mute only SMS or all messages. Makes more sense to unify both features instead of creating another GUI with basically a similar purpose.