I think it might be difficult due to world and quest mechanism. They're all out there in the world, so you get a call an initialize the quest before you enter the area. There are already quests you can enter before they're assigned to you (like due to insufficient SC or not being far enough in story) and mess up those areas (e.g. like with Cinema and Rogue, where if you enter it before to scan Tarrot, you miss half of the dialogue with Rogue).Actually it could be more fun to just receive one call from the fixers and to get missions go to see them in person...that would solve this phone calls problem,or maybe we could them for jobs to...
So to dismiss calls they also need to change how all gigs are handled - either block you out of all quest areas somehow (like fixer giving you a stolen door key or forged local network certificate) or remove the quests from the world before you start them, which would too cause a bunch of problems.