Have you tried the business betemax website like VoipTrade if they work with IOM mobiles. They used to work well on all UK numbers. If not Nindino also connects to all UK numbers for a very good rate. Nindino: Cheap calls to India, Pakistan, Srilanka, Saudi Arabia, USA from anywhere in the world

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has anyone tried Nindino's Phone to Phone callback function if it works ok?

I wonder if some of the cheaper Betamax providers will have stopped service to some numbers and others would still work, but I also wonder if the problem you've had is only on soem numbers

I called a +4476241... number using Justvoip a few days ago and it worked ok. I haven't tried 077000 though.

No, but I've seen Nyxfone discussed in one or two places, including an old thread here, and wondered about trying it. Given that the callback trigger number is the same these seem to be related

Note that some of these SIMs don't send caller ID information, so are going to be tricky to use with some other services

Nindino also can't access 004477000 numbers

I just want to chime in on this - I have an IOM number (+447924) from easyroam. Calling it via voipCheap now give a busy tone. I have used this in the past with VoipCheap without problems.

IOM 004477000 numbers aren't accesible from alsmost anywhere!

I am using voicetrading from betamax on ekit +44 number and this has no problems

it depends mainly from the network vendor of each number.. not the reseller (e.g ekit)
can you post some more digits?

voicetrading only accept business customers?

ekit number +44-7924 no problems

voicetrading is normally for business in the Eu, you have to supply a valid VAT number. You might also be able to register and non eu member