The case for buying shares of wireless company Sprint Nextel Corp is weakening as the company faces tough choices about upgrading its network, Barron's reported in its latest issue.

The magazine said investors were anxious about what path Sprint would choose to upgrade its network to next-generation speeds -- either spending more on an existing deal with Clearwire Corp or entering into a deal with someone like privately held LightSquared.

Investors may get out of the stock, Barron's said, if the company takes on much more debt or chooses an upgrade path that eats into future profitability.

Sprint shares closed at $5.43 on Friday. They are down about 8 percent over the last month, but still up more than 28 percent this year.

(Reporting by Ben Berkowitz, editing by Maureen Bavdek)

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