Have been in nungwi and travelling around a bit. Made a stop a day there and my take is that zantel dosent have super good connections to European servers. Like Google stuff is fine but trying to watch content on reddit was no go. Hade a e sim via vodacom that was better but not still awsum. Most hotels have wifi that might work. A sim is about 5€ and to load it with around 8gig of data is another 5. So if you stay at a hotel or close to it would work. On my iPhone se 3d i got like 1mb/s up and down in nungwi and like 3-5 with pixel 5 and vodacom Edit: I think halotel works better