If my device (smartphone/android) lost and i have backup the seed wallet.
How to import old wallet address?
Very good question. How would one import the wallet.dat for the phone app if phone was reset/crashed/bricked/smashed/thrown from a car window etc.
Wallet seed is not enough because private assets, such as blackbytes, are stored only in the wallet (exactly because they are private) and get updated every time you send or receive a private asset.
To secure against loss of the wallet, I recommend that you use multisig. For example, 1-of-2 multisig with one wallet on the phone, the other on a desktop computer. This way, the private assets will be automatically copied to the two devices.