Make sure that you purchase a cell plan through your preferred provider, that is either GSM or CDMA. When purchasing your plan, make sure you request a public static IP address, if possible. If they do not provide static IP addresses, it is still possible to access the ICX30 over the Internet, just a little more difficult, as your IP address will likely change often. Once your plan is setup, they will provide you with an APN Name that you will need to enter in the WAN configuration of the ICX30. Once that is entered and your plan is activated you should be ready to make a connection to the Internet. A solid NS LED is a good indication that you have Cellular connectivity, and access should be possible.
It is possible to access the ICX30 without a static IP address, just a little more difficult, as your address will be part of the general public pool, and will recycle often.