Hello!
I'm WHMCS admin user/developer already since v2.2 (somewhere in year 2006), did many template customizations, hacks & hooks, provisioning modules and payment gateways (last was The Ethereum payment gateway for WHMCS 7.5.2).
I would love to brain-storm, configure and help you tweak anything on WHMCS.
Once i clarify the events on which to send sms/calls, i will update my offer accordingly.
P.S: In the past i have integrated twilio to send sms on some complicated events (send sms for landlord once a tenant paid his bill - yes, i've tweaked WHMCS for one of my clients to use it as property management)
Looking forward working with you,
Mathew