No it isn't. In common with most other mobile networks, Smarty uses CG-NAT (carrier-grade network address translation) meaning you share an external IP address with other users, and it is not possible to make an incoming connection to your router from the internet.
The only UK mobile network which allows you to do this is Three, using the 3internet APN (note that if you set that APN on Smarty, you may get internet connectivity but your connection will still be CG-NAT-ed).
Depending on what you are trying to achieve, you may be able to use a workaround, for example, a service like Tailscale or ZeroTier. If you are wanting to run a web server on the standard ports you could use a Cloudflare tunnel.
