Cell service has been getting better on Kilimanjaro, but it still has a long way to go before you can make a phone call from any location on the mountain. You can expect to get reliable service once or twice per day on the trek, but most of the time you will be outside of any cell network. I recommend taking along a satellite messenger to keep in touch with friends and family back home. You can find wifi and reliable internet once you have returned from the mountain, but there is no wifi at all in any of the mountain campsites.