Country: UK
Carrier: EE
Monthly cost: £138/month (family plan for an iPhone X & Apple Watch 3 LTE for myself and an iPhone 8 for my wife - includes the cost of the phones/watch)
Data: 15GB (per phone)
Calls: Unlimited
Texts: Unlimited
Special feature(s): Data and call/text allowance can be used in the EU, price for roaming elsewhere varies. Data can be “donated” to another line on the plan. WiFi calling, free Apple Music (subscription and data allowance) for 6 months (not used)