USAir flies from Edinburgh to the US, at least seasonally, and you can get to Boston via Philadelphia or Charlotte. Miles earned on these flights can be applied to AA now, and will eventually end up there in any case. Miles earned on BA flights can be applied to the AA program (though not to the US program). When redeeming miles for award travel, BA should be avoided because of prohibitively high fees, but flights on IB (which flies BOS-MAD), AB etc. are fine.