Most lodges and tented camps now offer Wi-Fi, usually in the main area rather than the rooms, and usually adequate for messages and email rather than video calls. Mobile coverage across the northern circuit is better than people expect — Vodacom and Airtel reach much of the Serengeti — but there are real dead zones, and the Ngorongoro Crater floor is one of them.
A local SIM is cheap and easy: bring your passport, buy one at the airport or in Arusha for a few dollars, and a generous data bundle costs very little. It is far better value than international roaming.
Power is the thing to plan for. Tanzania uses UK-style three-pin type G plugs at 230V. Lodges have mains power; tented camps and mobile camps usually run on solar with a battery bank, and many switch the inverter off overnight, so charging happens during the day in the main tent rather than beside your bed. Every safari vehicle has 12V and USB sockets, which is where most people charge. Bring a spare camera battery and a power bank and you will never think about it again.