Can I send a promotion by text message rather than WhatsApp?

Yes. Text message now sits beside WhatsApp and the wallet card on Promotions → Channels, so you can pick it per promotion. It obeys exactly the same rules as the other two: your weekly cap, the hold that catches a customer matched by several promotions at once, the same excluded customers and the same sending hours. Your operator bills each text. Two things to weigh: a text carries no link preview and no formatting, and marketing by text carries an exposure that somebody ordering from you does not by itself cover.