I come from a family of pragmatic travelers who will often skip on "luxury" expenses, like a local sim card that makes one's smartphone usable while traveling through a foreign country. But with ready access to resources like maps, language translation apps, and Wikipedia, a functioning smartphone ought to be a priority when navigating a culture as distinct as Russia's.
Moscow is swaddled in strong, high-speed LTE signal available from a number of affordable providers. Look for company names like MegaFon and Beeline, which offer prepaid Russian sim cards compatible with your unlocked smartphone. I've paid as little as $1 USD per day for unlimited data.