The number of email addresses/SMS/phone numbers that can be added for alerts
There is a limit of 500 alerts per day for an email address. When your configured monitor is down , alert emails will be sent to all the email addresses associated with the corresponding monitor.
In case of SMS alerts, an alert SMS will be sent to all the mobile numbers mapped to the account. SMS alerts are charged at 1 alert credit per SMS. Each SMS will be counted separately and the number of alerts sent will be reduced from the total number of alerts available under the Alert Credits that you have purchased.
As for adding the phone numbers, you can add as many sub-users as you would want at no extra charge. Each sub-user can have their own phone number on which they can be alerted. Please note that the more numbers you add, the more alert credits will be used. Your billing will be only on alert credits, that is, every time an alert is sent, your alert credit balance will be deducted (2 credits for 1 phone call). Let us say you have 5 phone numbers to be alerted, for every alert 10 alert credits, (5*2) will be deducted.
You can purchase additional alert credits as and when required. 100 alert credits are priced at US $20.