You can make telephone calls using phone cards and buy postage stamps at Telecom Cook Islands (weekdays 0730-1600), north of Mapumai village. Internet access is available.
The Air Rarotonga office is a block back from the CICC church in the center of the island. There are four flights a week from Rarotonga, plus weekly services from Aitutaki. Most of the guesthouse owners provide airport transfers.
Atiu Villas and some of the other places to stay rent bicycles/scooters/jeeps.
The Humphreys family of Atiu Tours leads kopeka bird cave tours and half-day island tours (they also rent rooms). George Mateariki does a bird-watching and bush walk.
These tours are worthwhile as nothing is signposted on Atiu and finding your own way is hard.