SMS Sending Dynamically

Is it possible to send sms on save of lead without going through backend but just from front-end. Like without using hooks or anything related to backend but just frontend

Try this:
You can use following method in py on validate event. but you have to pass parameters like receiver no and message.
from frappe.core.doctype.sms_settings.sms_settings import send_sms

    receiver list = [91**********,91**********]
    send_sms(receiver_list, cstr('your message'))

This will only work if you have done sms settings.