Yes, that is possible. You can receive push notifications (but not calls) to as many phones as you like.
All you need to do is simply login with the same account (your phone number that you used to setup Monimoto for the first time is your account ID).
Firmware 1.1.5.0 and lower
All the auxiliary phones will have limited access to Monimoto (it's called cloud access). For example, you will not be able to configure Monimoto settings from them but you will receive push notifications to all phones in case of alarm.
Home and Events tabs will look the same.
Device list tab
Restricted settings view
Firmware 1.2.3.0 and higher
You will receive push notifications and you will be able to configure Monimoto settings in the Settings tap just like in your main phone.
IMPORTANT: Phone calls will only be received to the original phone number that was used to setup Monimoto, or as set in settings!