The easiest way of activation of the card is to ask the seller to activate the card when buying it. Or immediately after purchase to insert the card into phone, enter the pin and activate the card by following the instructions on the subscriber's reference.
But you never did. Nobody forbids you to come after some time in the salon MTS and ask them to activate the card. If it isn't blocked for non-payment or for any reason specified in the agreement, you will be in a matter of minutes.
You may have to write a statement, so bring a passport. In that case, if you owe the operator will have to pay for calls made on credit.
If this does not suit you, there is absolutely no time for a trip to the salon MTS, try another way. Try after insert SIM card, dial any short number MTS - *111# call.
If failed, please call 0890 (or 88003330890), and name the number that are unable to make a call. In any case, keep on hand your passport and the contract with the operator (may be needed).
It should be noted that it is better to entrust the activation of the card to the seller on the day of purchase, so you do not end up in a difficult situation. This is especially important to do when buying cards on the rack at the Mall or on the street. Sometimes a seller can be a fraudster.