In flight weather can be observed (most airliners have weather radar onboard) and the pilots can check on weather along their route with controllers and at the destination or in specific places by electronic inquiry.
In-flight weather by radio is an option but it’s a manual thing. And the airline may not be set up to use that except an emergency situation.
It is a requirement - AWIS/ATIS and ATC/Tower (all via radio) can provide weather information at airfields, and a lot of instrument approaches do require certain readings before an approach can be commenced.
There is also the PIREPS (Pilot Reports) system where pilots report actual weather conditions as encountered by an aircraft in flight. Some aircraft have automated weather reporting systems (AMDAR).
I don't think the equipment to receive weather updates is on the Minimum Equipment List, but if dispatch couldn't even update over the radio then I would imagine they would start diverting flights. This is just a guess, hopefully someone with more knowledge can jump in here.
It depends on the airframe - but I believe for Airline Transport category aircraft a storm scope and a few others are required.