The virtual number space breaks into a few categories, each with a catch worth knowing. Google Voice is the best known: a real number that handles calls, texts, and voicemail over data anywhere in the world. The catch is you generally need to set it up from a supported country, and porting your existing mobile number into it involves a fee and some steps, so arrange it before you move abroad.
Skype-style paid numbers let you buy a number in various countries and receive calls in the app, useful if you want callers back home to dial a local-to-them number.
That last point is the big one: no virtual number fully replaces a real mobile number for bank OTPs.