SIM900 / ATMEGA 2560 / Arduino 1.8.4

Good morning

We need to update the obsolete SIM900 2G (SIMCom)

on a board based on ATMEGA 2560 / Arduino 1.8.4

What new modem (to send only sms, but in rural areas) ?

Interest of changing also the 2560, rather than trying to minimize the Hard and Firm

transformations ??

If you had gone through this experience, would be of a great help

Merci. Xavier