There are 4 methods commonly used for wireless internet access:

1. Through a pre-paid voucher (bought on site, or previously).

2. Credit card sign-up online (one-off or subscription).

3. Longer-term subscription, with roaming arrangements.

4. Roaming arrangments with ISPs or telcos.

Most hotels, in my experience, offer at least 1 and 2. Some only 1, which is very irritating when you need to download your mail at midnight.