Response DueBy Time question on Requests in Service Desk Plus?

Response DueBy Time question on Requests in Service Desk Plus?

Is there a way that response time can be set when I add a work log or something other than sending an email from the request screen?
 
It seems that is the only way I can get the response time set, is by sending an email from the request, but sometimes we call the customer and leave a voicemail and I want that to count as a response time?
 
Just curious we are getting ready to start using this in our production environment but I don't want to fail SLA's because I cannot get this field updated.
 
Thanks for any info...
Kevin

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