where a player pushes 350 simultaneously whilst saying "I call 350" this would be governed by the house rules on the method deployed for betting and raising (forward motion V chip release), for example ours is chip release, therefore it would still be a call of 100, as the chips have not yet been released at the point the player stated "I call 350" although we do have a condition that a reaction caused by forward motion may be binding. Where forward motion is used as the method for betting and raising it would likely be a raise to 350 total, although it would be highly dependant on the situation.
Another careful consideration must be given to what the intent was, the intent was to make the bet 350 total, if the SB has folded and the BB already has his chips in by the time we get to the table I would likely let the unclear action go as a raise, as removal of the 250 would not be in the best interests of the game - again this returns to forward motion causing a re-action. If I was called to the table and the unclear bet was still awaiting clarification and the BB player has not yet acted, or indeed the SB, I would rule it a call on most occasions, in order to protect the SB and BB from the actions of the Button player, the key for me would be to protect the SB and BB whatever way I call it.
Regards
Stuart