Does convoke allow you to tap creatures with summoning sickness to reduce a spell's cost?

Convoke (CR 702.51) is a static ability that modifies how you pay for a spell. When you cast a spell with convoke, you may tap any untapped creatures you control as part of paying that spell's cost — each tapped creature either reduces the cost by one generic mana or contributes one mana of that creature's color.

Summoning sickness (CR 302.6) only prevents a creature from attacking or from activating abilities that include the tap symbol (⟨T⟩) or untap symbol in their cost. Tapping a creature to pay for convoke is not activating an ability — it is part of the spell's casting process as defined by CR 702.51a. Therefore, summoning sickness does not interfere with using a creature for convoke.

CR 302.6 specifically states the restriction applies to 'activate abilities with the tap symbol.' Since convoke tapping happens during the process of paying a spell cost (CR 601.2h), it falls outside that restriction entirely.

Concrete example: You cast Siege Wurm (a convoke spell costing 5GG) on your main phase. You have a 2/2 creature token that just entered the battlefield this turn (summoning sick). You can tap that token via convoke to reduce Siege Wurm's cost by one generic mana, even though the token couldn't attack or tap for its own activated abilities.

In summary: summoning sickness never blocks convoke usage. Any untapped creature you control, regardless of when it entered, is eligible to be tapped for convoke.