Does Haste allow a creature to activate tap abilities the turn it enters the battlefield?

Normally, a creature cannot attack or activate abilities that require tapping ({T}) on the same turn it comes under your control. This restriction is defined in CR 302.6, which states that a creature cannot attack or use a {T} activation if it has been under your control since the beginning of your most recent turn — unless it has Haste.

Haste (CR 702.10) specifically overrides CR 302.6 for the creature that has it. This means a creature with Haste can both attack and activate any ability with {T} in its cost immediately upon entering the battlefield — even during the very turn it arrived.

It is important to note that Haste only bypasses the 'summoning sickness' restriction tied to tapping costs and attacking. It does not help with abilities that don't use {T} in their cost, since those are never restricted by summoning sickness in the first place (CR 302.6 only applies to {T} and attacking).

Concrete example: You play Village Bell-Ringer (which has no Haste) — it cannot use a {T} ability this turn. But if you play a Llanowar Elves (which has Haste), you can immediately tap it for {G} mana the same turn it enters the battlefield.

So as long as the creature has Haste when it tries to use its tap ability, summoning sickness is not a barrier, no matter when it entered this turn.