Thank you for your email and for showing interest in purchasing TRU. As long as your phone is unlocked, i.e. you can put any SIM card in it, no matter which service provider it is, you will be able to use your Tru SIM card . When you activate the SIM card, you will be automatically given a number which will be assigned to your SIM card as your main number which depends in your country of residence. If, however, you decide that you would like to purchase any secondary Tru numbers for your SIM card, it will cost you £5 or $8 per month. There is no obligation to purchase any secondary numbers, it's just that you may find it easier for people to contact you if you have numbers from more than one country. Credits do not expire as long as the account is active. Denominations for top-ups 15,30,45,75 and 150. To keep the account active you need to send an sms or make a call once every 90days. I hope that this helps.