* Zynga shares slide after warning, Facebook slips
* Sprint could counterbid on PCS -sources
* Futures up: Dow 20 pts, S&P 1.6 pts, Nasdaq 6.5 pts
By Rodrigo Campos
NEW YORK, Oct 5 (Reuters) - U.S. stock index futures inched up in thin trading Friday, after four days of gains on the S&P 500, and ahead of a government payrolls report expected to show a tick up in hiring last month and a slight increase in the unemployment rate.
A positive market reaction to the jobs report could drive the S&P 500 to its highest close since December 2007, about four points above Thursday's close.
"Investors could use weak data as a reason to take profit after the four-day run," said Andre Bakhos, director of market analytics at Lek Securities in New York.
The payrolls data, due at 8:30 a.m EDT (1230 GMT), is forecast to show 113,000 jobs were created in September compared with 96,000 in August. The unemployment rate is seen at 8.2 percent, against 8.1 percent in the previous month.
S&P 500 futures rose 1.6 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures rose 20 points, and Nasdaq 100 futures added 6.5 points.
Zynga shares fell 22 percent in premarket trading after it slashed its 2012 outlook for a second time, fanning doubts about its ability to halt a steep decline in earnings. Facebook, which derives over a tenth of its revenue from fees paid by Zynga, saw its shares fall 3.3 percent.
Sprint Nextel is considering making a rival bid for MetroPCS Communications, which agreed Wednesday to a merger with Deutsche Telekom's T-Mobile USA, according to people familiar with the situation.
U.S. stocks rose on Thursday following encouraging U.S. data and comments by European Central Bank President Mario Draghi on tools to tackle the region's debt crisis and in support of the euro.