MailChimp - MailChimp is the best way to design, send, and share email newsletters.
Postscript - Like Mailchimp for SMS
Brevo - Innovative online Email Marketing solution to manage your contacts, create & send your newsletters and track your results. More than 80 000 clients. Best prices and attractive features.
Tatango - Tatango is a mobile messaging platform for agencies.
Campaign Monitor - Email marketing software built for designers and their clients to run successful email campaigns.
Flowroute - Flowroute provides direct access to telephony resources - such as calling, messaging (SMS & MMS), call routing, SIP Trunking and Communication APIs.