ATo in BB with BTN limp and SB complete

[hagbard celine]

Full Tilt Poker
No Limit Holdem Tournament
Blinds: t6000/t12000
(Ante: t1500)
6 players
Converter

Seat 3: BTN (195,665)
Seat 4: SB (142,692)
Seat 5: Hero (381,456)
Seat 6: (424,866)
Seat 7: (228,024)
Seat 8: (187,551)



Pre-flop: (6 players) Hero is BB with T[img]/images/graemlins/diamond.gif[/img] A[img]/images/graemlins/heart.gif[/img]
3 folds, Button calls t12000 <font color="aaaaaa">(pot was t27000)</font>, SB calls t6000 <font color="aaaaaa">(pot was t39000)</font>, Hero ?

BTN has been open shoving, and I'm pretty sure this is his first limp. I'm really not worried about SB. Should I just be shipping it in? If I raise, am I calling a shove?