* Sprint agrees to buy T-Mobile US - source
* Futures up: Dow up 28 pts, S&P 2 pts, Nasdaq 3 pts
NEW YORK, June 5 (Reuters) - U.S. stock index futures were slightly higher on Thursday as investors awaited what is expected to be a significant easing move from the European Central Bank.
* The ECB is poised to drag interest rates below zero on its overnight depositors in a move to push banks into lending, and it may also launch a loan program for banks with strings attached to make sure the cash gets out into the economy.
* The widespread expectation of the monetary policy move has kept pressure on the euro in recent days, while keeping yields on government bonds low. Earlier on Thursday, Spain auctioned 3- and 5-year bonds at record low yields.
* The risk for equities is on the downside. Expectations for the ECB easing were running high, having already fuelled risk appetite in recent days and supported the drift higher in the benchmark S&P 500 index, which closed Wednesday at a record high.
* S&P 500 e-mini futures edged up 2 points and fair value - a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract - indicated a slightly higher open. Dow Jones industrial average e-mini futures rose 28 points and Nasdaq 100 e-mini futures added 3 points.
* Sprint has agreed to pay about $40 per share to buy T-Mobile US, a person familiar with the matter told Reuters on Wednesday, as the long-contemplated deal to merge the third- and fourth-largest U.S. wireless carriers advances. Sprint shares, regularly volatile in premarket trading, were up 5.1 percent in very light volume. T-Mobile US rose 1.8 percent.
* On the data front, the Labor Department's weekly reading on applications for unemployment insurance is due at 8:30 a.m. EDT (1230 GMT). The number is expected to rise to 310,000 from 300,000. (Reporting by Rodrigo Campos; Editing by Chizu Nomiyama)