Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude
Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action
Company Policy; Human Factors; Procedure
Our flight had just leveled off at FL250.  There was a similar sounding call sign on the frequency as well.  I (First Officer) was Pilot Flying and the Captain (Pilot Monitoring) had just started giving a PA to the passengers.  As soon as the Captain started his PA; Atlanta Center gave instructions to what sounded like [our call sign] to climb to FL280 with an expedite through FL270.  As soon as I acknowledged the clearance; I noticed we had traffic approximately 1;000 feet above us at our 11 o'clock position at about 10-15 miles.  I thought it unusual for ATC to issue us a climb clearance with traffic that close and 1;000 feet above than us.  I knew [a similar call sign] was also on frequency so I called ATC back to verify the climb clearance for [us].  They did confirm it was for us so I went into an open climb for best rate climb through FL270 with a level off at FL280.  Once we started climbing; I noticed the traffic at our 11 o'clock starting to close in on us.  As we approached FL260; ATC instructed us to turn 15 degrees to our left to avoid conflicting traffic.  With the conflicting traffic at our 11 o'clock at approximately 500 feet higher than us; I thought the controller had erroneously meant for us to turn 15 degrees right instead of 15 degrees left. I immediately asked the controller to confirm 15 degrees left due to the traffic.  Right after I asked the question; we received a TCAS RA that instructed us to descend in order to avoid the conflicting traffic. Simultaneously; ATC instructed us to descend and maintain FL250.  I disconnected the autopilot and complied with the TCAS RA instructions to descend.  The Captain came back from making the PA and searched for the conflicting traffic.  He stated that he did get a visual with the conflicting traffic passing us at the 8 o'clock position as we descended in accordance with the TCAS RA. We leveled off at FL250 without further incident.  I did not inform ATC that we were responding to a TCAS RA because I was focused on flying the aircraft and complying with the TCAS instructions.  The Captain had been making a PA and so he was not listening [and] talking to ATC when we received the TCAS RA.I believe a factor in this incident was that ATC had given us a clearance to climb up to FL280 with the conflicting traffic where it was.  We were at FL250 with traffic at approximately 11 o'clock and 1;000 feet above us.  I even confirmed the clearance was for us since I thought it odd we were given a climb clearance with the traffic where it was.  ATC should have kept us at FL250 and not given us instructions to climb until the conflicting traffic had passed behind us.I also believe the similar call sign contributed to the confusion factor.  Hearing the controller issue instructions for [us] to climb when we had traffic in front and only approximately 1;000 feet higher than us led me to believe that she may have meant the instructions for [the other flight].  I delayed the climb to confirm that the instruction to climb was for us.  If I had started the climb when she first issued the instruction; we might have avoided the TCAS RA.  I however wanted to make 100 percent sure she meant for us to climb though so that did cause a delay in our aircraft climbing.  I recommend [our company] consider discontinuing similar sounding call signs around the same hubs with similar takeoff and land times.  I have noticed many times that my flight number on a particular flight is off by 1 number from another flight operating in the same airspace.  Having dissimilar sounding call signs would cut down on a lot of the confusion for both the pilots and the controllers.
An A319 First Officer reported responding to an RA during climb; citing similar call signs as contributing.