A sweepstake is a type of contest where a prize or prizes may be awarded to a winner or winners. Sweepstakes began as a form of lottery that were tied to products sold. In response, the FCC and FTC refined U.S. broadcasting laws (creating the anti-lottery laws).
Yes it is permissible to enter in a giveaway as far as there is no gambling or lottery involved.
Yes it is permissible as far the business is lawful.
If the prize is provided by the money collected from the message rate, then it would be a gamble and is not permissible.