You can use your cell phone while in Moscow and St. Petersburg, however. And you can use one of numerous internet cafes too.
Activating your cell phone for international roaming
You can use your cell phone in Russia, but then you need to contact your cell phone service provider before your departure to Russia and ask them to activate "international roaming." Please note, it could be quite expensive, up to 3 dollars a minute.
Tip: if you buy a local sim card you can save money on calls in Russia. International calls will cost about the same as calls made in roaming ($2-3 a minute). Ask your cruise director if you want to purchase a local sim card.