The answer to this is a complex one. The first thing we need to remember is the generation gap. The younger set accepts texting as a natural order of business. However, many older people do not. If your boss is younger, then it's more likely you'd be able to. Secondly, check to see if your boss actually allows texting, especially if they never gave you their contact information. If they didn't give it to you, then don't ask around for it, send an interoffice email instead.