You need an active membership and cash credit on your account to pay for incoming and outgoing calls and outgoing texts.
It's quite expensive though - €1.99 per minute to make calls, €1.89 per minute to receive calls and 39c to send an SMS (long messages could use more than one SMS)!
48 don't support data while roaming abroad so you'll only be able to access the internet and other online services while connected wifi where available.
If you have an iPhone then you'll need to be aware of this issue:
Hope this helps.