Is roaming free in Hong Kong with my Mainland China or European SIM card?

No, this is a crucial point for travelers. Although Hong Kong is a Special Administrative Region of China, it operates under separate telecommunications regulations. Therefore, your Mainland China SIM card, even if from a major carrier like China Mobile, will likely incur roaming charges. Similarly, EU 'Roam Like at Home' plans do not extend to Hong Kong. Using your European SIM here will result in significant roaming fees. EastESIM provides a dedicated Hong Kong plan, offering clear pricing and reliable access to local networks like SmarTone or CSL without any nasty surprises.