With Business Xtreme Plans, you may avail any device available from the application form under a 12-month contractual option. 
Device add-ons are optional and are sold as per their standard retail price. You can subscribe to the device add-on when activating the base plan or even after it has been activated.

Business Xtreme would come with an extensive list of add-ons for extended local and international minutes, local or roaming data add-ons. View list of add-ons here

If you are upgrading or downgrading within the Business Xtreme before 2 months, an early contract termination/service cancellation would apply. This would mean a one-time charge of the monthly rental would be charged. In the case that the online offer has been redeemed, you can upgrade to plans only after the completion of the promotional period of two months with the contract being reset and exit charges being applied. Subscribers of Business Xtreme 900 & 1200 would need to complete the 12-month duration until they upgrade or downgrade.

Exit charges applicable for device and base plans as per the following:

       (i) Exit from the Base Plan only – 1-month of base plan rental fee. 
       (ii) Exit from Base plan with a Device - 1-month base plan rental fee + remainder months of rental for device.

Yes. You can choose to subscribe independently to the Business Xtreme Plan without devices.

Unlimited allowances are better defined as adhering to the fair usage policy or capping of minutes applicable.

You can check your balance allowances by simply dialing *140#