They do not list charges or uses per day. Only that the first Elemental has to die (or be dispelled or dismissed) before a new one can be summoned. The summoning only requires one round so you could essentially keep summoning huge Elementals and send them to attack a small fort or town one by one until they crush it and all defenders. With enough mobility and sneakiness you could destroy a string of targets every day.
I mean items like Bowl of Commanding Water Elementals, Brazier of Commanding Fire Elementals, Censer of Controlling Air Elementals, Stone of Controlling Earth Elementals. Here's a link to all: http://www.d20srd.org/srd/magicItems/wondrousItems.htm#bowlofCommandingWaterElementals
PS: Do the Elementals summoned have a duration? It says:
A new elemental requires the bowl to be filled with new water, which cannot happen until after the first elemental disappears (is dispelled, dismissed, or slain).
Doesn't mention duration ending, or expires.