Mailchimp mobile app integration, VOIP integration, creation possibility to receive the calls onto mobile app and callingg leads

We are currently starting to use Mailchimp business account to collect the leads and segment those and then contact the leads. From our experience the conversion rate of the leads after approximetely 5 min drops tremendiously. With this project we are looking for a person who could set the system upon which the lead will come onto mobile version of the mailchimp and have loud notification similar to Whatsapp or SMS nofication and upon opening the notification to be able to phone the lead by clicking onto phone number however call should pass via VOIP and we should be able this way to analyse incoming and ourgoing calls and record the calls to know how well our sales managers performed.
Please send with you bid exact experience you are having with curent system with some examples. Send also best possible VOIP integration to be cost effective and at the same time have good sound quality.
Sending the autoresponder in case if clients can not reach us. With possibility to leave the message.