T-Mobile UK is blocking calls to mobile VoIP start-up Truphone. That's a serious issue which caused interesting discussions and points of view. As GigaOM puts it: "CellCarriers fear mobile VoIP planet". That's more or less how I see it as well.
After the fixed line carriers got shaken up by VoIP now it's the mobiles' turn. T-Mobile UK tries to defend its well established business. Maybe Truphone shouldn't have said that they now support VoIP over 3G. It's the old fear of the traditional mobile carriers and one of the main reasons why they kept the mobile data rates sky high in the last years: To loose their comfortable voice revenues.
Rebtel's CEO Hjalmar Windbladh explained to me not so long ago that mobile carries pay only 0.8 Cent to connect a call between Germany and China. But they charge 1 Euro or more from the customer, depending on his contract. These big margins would get lost with VoIP over 3G and maybe that's the reason why T-Mobile UK wants to dry out its competition before it gets too strong.
But this is like trying to cut all of Hydra's heads. It's not only Truphone which is offering VoIP over 3G and over Wifi. It's also Fring, Wifimobile, Mobiboo, Yeigo, aql and thousands of other companies worldwide. In fact every SIP based VoIP provider can do a quite similar job like Truphone. It makes no difference if you install your SIP login data into a mobile phone or an ATA or a soft phone.
I especially like it to have my fixed line home number ring on my mobile phone. For that I use Wifi or a call forward over GSM. Outgoing calls are nearly free or free via calltrough or Wifi.
Just like at Truphone.