Your SIM card phone number starts with +372 by default. In addition to that, you can choose to purchase a UK phone number (+44) or a US phone number (+1).
If you purchase a US or UK number, it will become your primary phone number for calls&sms. Your default +372 number will still work for incoming calls. Data usage is not affected by phone numbers. Please note that UK numbers can receive calls and SMS. Incoming call 0.20$ or 0.15€/min. Incoming SMS is free. US* numbers can only receive calls outside of US. No SMS service. No incoming or outgoing calls&sms available in US because U.S. wireless carriers have started shutting down their 3G networks. Incoming call 0.20$ or 0.15€/min
Here are all the countries you can travel to when you select this data plan: