Yes. If you use the same email address and the same password the accounts will be linked and you can quickly switch between them in your account area.
Phone credit cannot be shared between your phone numbers.
You will be emailed a default password for each new account so you will need to change these to be the same password after activating the SIM.
If you wish to place an order for multiple SIMs (e.g. more than 3 or 4,) please contact customer services and we can arrange this for you with one initial payment. We can also link these at that time, if you would like.