I am planning to send alerts from vROPS to a SMS server, so that users will get alerts in their mobile phone ? What are the possibilities ? What kind of customizations needed in vRops
Depends how your SMS service will accept alerts.
There is a couple of options i can think off. Can send an email to the service on particular alerts (by default may be bigger than what is allowed in SMS), or SNMP trap.
Can send an email to vRO which then parses it and sends another email to the SMS server or rest call to the service. with vRO in the middle most things can be done.