If cash becomes obsolete, what form of cash-in service do you think would be available beforehand?

Assuming that with technology and sustainability boom that physical paper money will eventually become obsolete (say in next 100 years), what do you think would be the best way/method for people to “cash-in” their physical money? How would government deal with transition problems? How long should the cash-in service last to prevent the continuing money laundering, terrorist funding, etc. before it becomes completely value-less?

(Also, would cellphone technology be developed to even make credit cards obsolete? )