The microcontroller itself requires no maintenance at all if used in reasonable temperature range. The same applies to a GSM module in case of its usage. However, a mobile phone has a few drawbacks and needs to be maintained every now and then.
First, SMS inbox is filled up in mobile phone as time goes by. Technically, all incomming messages are erased by microcontroller logic as soon as they are processed. But if SMS was not handled correctly (for instance, if SMS encoding is not supported by the microcontroller), it won't be deleted. Such messages must be deleted manually.
Second, pictures taken by Siemens CX65/70, are located
in a read-only part of phone's filesystem and cannot be deleted by a
The only theoretical way to overcome the obstacle is to navigate through the
phone's filesystem by means of keypad emulation which is considered unpractical
due to potentically error-prone approach and thus it is not implemented in current
microcontroller's firmware. All in all, the folder containg pictures taken by
phone's camera must be clean up manually from time to time. Depending on model
revision and number of already installed applications, Siemens CX65/70
is capable of holding up to 100-130 VGA pictures.
Third, as the mobile phone is constantly recharged and in most cases exposed to temperature drops, it minimizes battery's lifetime and leads to its untimely degradation. There is only one solution for the problem: battery replacement.
Fourth, if source of backup power supply is used, its batteries must be replaced when they are run out of energy. Current hardware implementation is not capable of battery charging or measuring the battery charge level yet, it might be implemented in next revisions.