Incoming calls have not been possible on my sim since Friday. Caller just gets a tone than the message that the call cannot be completed as dialed. I am seriously beginning to question the reliability of Telna. One day last week I received an email that detailed some kind of major outage that they suffered, that took down their entire system. I am not sure if this is related to that.

I travel out of the country for 2 weeks on Wednesday. My plan was to forward my US number to my Ekit and/or Telna, since it's important that I am reachable. Telna just made that decision easy.

If I had to pick one issue that I thought was the most serious for Telna, I'd have to say it's reliability. There have been times when it was difficult to get the SIM even to register on T-Mobile. I doubt I would travel with TelnaMobile without also having a backup plan. Of course, that's true of any roaming solution. Spare phone, spare unactivated SIM, backup service, etc.

I am currently in Nigeria. Using a local MTN sim and Ekit. I am not surprised any bit that my telna did not register on any network and is now showing unregistered sim. Even though it was working find before I left the US.

Sometimes it takes several power-cycles and a wait before it will register. I think it has something to do with the multi-IMSI SIM they use.

Absolutely! Thanks for mentioning this. I power cycled and a few minutes after powering up, it registered, and calls were possible.

Do you know to which networks the IMSIs are tied to? How do you control on the SIM which IMSI to send to the VPLMN and how can each IMSIs be used by the same MSISDN. Wouldn't the HLR return an error? I thought 1 MSISDN=1 IMSI. Unless each MVNO agreement is tied to a different HLR but CDRs are consolidated per MSISDN for billing.

Once long ago I read the details of how multi-IMSI SIMs work. I've forgotten the details. However, I know that at some point the phone tells the SIM the MNN of the network it is attempting to register on. The multi-IMSI SIM can change its personality based on this information. There is really no way for the user to get the SIM to change its behavior. It all has to do with the networks the phone sees when trying to register.

I don't know much about this, but perhaps things vary in the way they've been implemented by different providers

Some multi SIMs come with instructions which mention prefixing the PIN, so one would use 2xxxx or 3xxxx to select the alternate identities, and the 4 digit version will either select the first or the relevant default action.

I don't know whether this applies to all such SIMs. For some types of older phone this is actually necessary whereas for most it's optional.

I have an ekit SIM which recently arrived. Tried out in the UK only so far, by default it selects its Jersey ID, which seems to register only on Orange here. If I prefix the PIN with 2, it selects the Manx ID which roams all UK networks. I haven't tried the 3 prefix for the US ID., but I assume no roaming here.

Interesting. Since it's in the PIN, it sounds like a STK is running in the USIM software enabling what IMSI to use. Otherwise, automatic selection based on the available PLMNs and in order of the PRL (cheaper first of course!) in the unlikely case where 2 roaming networks are available but from 2 MVNO agreements. But being able to force one particular identity vs the others could be useful if the primary one is unreliable for instance.

Who offers the most IMSIs?

Sorry to say - This sim has proved to be too unreliable for my liking. Have not been able to reach the phone in the last hour. Message sometimes says the number is not reachable and sometimes it says the local number is unassigned. I was talking to my son on the phone earlier today. I can't depend on this thing. Have to get my son another sim.