Sprint (NYSE: S) sure had a big week last week.

The two major announcements for the third-largest domestic wireless carrier were that it would finally be getting in on Apple's (Nasdaq: AAPL) iPhone 4S action alongside larger rivals AT&T (NYSE: T) and Verizon (NYSE: VZ), who have commanding leads already built in the iPhone market. Sprint will have to compete vigorously to steal share from these giants. Sprint also announced it would be pursuing an aggressive rollout of its 4G LTE network, leaving Clearwire (Nasdaq: CLWR) out in the rain with its WiMAX network. Both of those are strategically sound moves to make. The real question that's been weighing on shareholders as of late is can the company afford it?

As of last quarter, Sprint's balance sheet was carrying almost $4.3 billion in cash and short-term investments. The company owes a total of $18.5 billion in long-term debt and financing and capital lease obligations, of which nearly $2.3 billion is current and due within the next year. These figures are as of June 30, before last week's announcements.

The Wall Street Journal had reported that Sprint had committed to buying 30.5 million iPhones -- roughly $20 billion -- from Apple over the next four years and that the deal would fail to generate a profit until 2014. There were also rumblings of exclusivity, but those predictably turned out to be bogus. Exclusivity would have tacked on another couple billion to the price tag. Lacking any official details, let's just simplify the cost to $5 billion per year.

Sprint said it plans on spending $10 billion on its network expansion in 2012 and 2013. Meanwhile, Sprint will continue supporting and selling WiMAX devices through the end of 2012, but you can expect it will ditch the technology as soon as possible. Add $5 billion per year to our count.

So we're up to an estimated $10 billion in costs in the first year alone between the iPhone addition and network upgrades. It's no wonder that the stock rallied on the initial good news, only to tank once costs came into the picture. Sprint is going to need to raise money, either through selling even more debt or raising dilutive equity capital. Neither scenario is particularly pretty for shareholders.

Don't forget to add Sprint to your watchlist to see if it can come up with the dollars that it needs. Sprint doesn't pay a dividend like its larger rivals, which can be an important component of any portfolio. AT&T's dividend is the only reason I own the stock. Click here to get access to a report on 13 high-yielding stocks you can buy today.