DID Logic has hundreds of on-shore and off-shore UK call center deployments. Customers report better ASRs (average seizure rates) to the United Kingdom networks than they’ve ever seen before with any VoIP provider. If the number exists, your call will get established (unless the number is occupied). You get higher agent efficiency – which means less time spent redialing, and fewer leads missed.
Our focus is on quality, and we invested significant amounts in maintaining direct routes exclusively. Grey route means G729 codec unfortunately. If your agents are involved in outbound sales, their leads capture rates are gravely affected by sub-par voice. G729 cuts of major portion of human voice frequencies to save bandwidth (and this is why it's an economy, grey route).
It's still an OK line, you can even hear the other party well, but the spectrum isn't there, nuances are lost, and even your brightest and talented employee will not sound as persuasive to the lead. You may be using G711 to your current supplier, but if they call it "grey" then they inevitably have to backhaul it via G729 to some other aggregator. This makes matters even worse as transcoding is now involved. We avoid transcoding:it's G711 all the way from the originating party to the TDM circuit.
Please feel free to contact us via email with a short summary of your UK deployment, and we will be happy to recommend one of our many tried-and-tested setups. The DID Logic trunk readily supports Asterisk, Freeswitch, 3CX, Nortel and the majority of other SIP-based PBX products – both software and hardware-based.