I like how easy it is to create integrations, you can use any language or tool for this task (eclipse/code).
It's free of charge until 50K calls per month are used; then we pay only 10 cents / call if our customers do not have their own cloud-based service provider in place yet! No other solution offers such great flexibility with so many providers at hand all over Europe - which makes life easier when selecting partners as well!! Nothing specific but there were some problems during development time where one had no clue what was going wrong because they could never reproduce these errors locally due to missing certificates etc., hence having access from various locations helped quite alot here too. We solved mostly business process related issues by integrating them into TTI via APIs using Java API Gateway services provided through teranetworks.