Generally, you'll have the same IP address for very long periods of time. However, I travel a lot and demo Azure at many different locations. It's quite easy to quickly add an IP address through the Azure portal. You go to the server. When it opens, it opens with the properties blade on the right (normally). There you'll see firewall. Click on that it'll open another blade. Right at the top it has a button, "Add Client IP". It will capture the IP address that you've connected to the portal with and you can easily add this to the firewall. Be sure you hit the save button so that it applies it. Pretty painless.

Real world, not a test or dev system, you'd want either a fixed IP address, or to assign a known range that your IP will fall within. Or, you'll be connecting from within Azure, so you'll be inside the firewall.