Show HN: Dtmf.io – virtual phone numbers from 50 countries, and SIMs in the UK | Hacker News Reader

Show HN: Dtmf.io – virtual phone numbers from 50 countries, and SIMs in the UK

dtmf.io

44 pointsdtmf-io27 comments

How do you plan to prevent abuse and fraud? This seems like it could attract a great amount of misuse.

And to follow up with that, do the carriers know what you're doing? The reasoning behind SIM cards is it is a hardware security device not unlike a payment card such as a physical debit card that ensures someone has to have the actual device to access the network. This service seems to disagree with that notion.

> How do you plan to prevent abuse and fraud? This seems like it could attract a great amount of misuse.

Exactly. In addition, in some countries (e.g. Germany) your client is required to have a physical address [1] not only in the country, but also in the area where they get their number.

[1] "Address" being a place where they can receive snail mail AFAIK

We comply with these regulations. To get a German landline number via our service, you must provide proof of an address in the same locality, as well as proof of ID. We supply this to the regulator, and once they approve it, we provide the number.

Many countries do not have these requirements, and for these countries you can just "click and buy".

Out of curiosity how do you verify these things?

We only verify them for completeness; then we submit them to the relevant regulator and wait for them to give the documents the OK. We don't assign the phone number until we get the OK from the regulator.

In the UK, a SIM card can be purchased without registration. We simply allow you to do that online and give you remote access to your phone (modem). One SIM card and one modem is used by one customer. It isn't really any different to walking into a shop and buying a phone and a SIM card.

How do you get the numbers? (Or, bluntly, how do I distinguish this from a productized SIM-swapping operation? Is it significantly cheaper than that would be? Or significantly more expensive?)

The virtual numbers come from a few different suppliers, one being Twilio for example.

The physical SIM numbers are infrastructure that we built, using racks of GSM modems, SIM card switching devices, and our own software to manage everything. The SIM card switching devices reduce maintenance requirements since when a customer no longer needs a SIM, we can electronically switch the modem to a new SIM without needing to visit the datacentre. We just have to go every so often to replace the used SIMs before the pool runs low.

Wouldn't number verification systems (for example, Facebook) eventually start blacklisting your numbers? I have seen this happen with VOIP numbers. Do you have a plan to tackle this?

The physical SIM numbers are SIMs from major UK providers, and are never re-used (for clarity: if you buy a SIM number, you get a SIM that has never been used by anyone else, and it will never be used by anyone else after you).

From the perspective of a number verification system (or anything else sending an SMS to them), they are completely indistinguishable from a mobile phone and prepaid SIM, since that is what they are.

The virtual numbers, while also never re-used, are often blacklisted by services that do SMS verification due to coming from a range designated as "VoIP" or "virtual", and we explicitly disrecommend their use for verification, although some people do use them with varying amounts of success since they are cheaper than the SIM numbers.

> it will never be used by anyone else after you

This isn't true; UK mobile numbers are re-used after a period of inactivity by the operator themselves.

Unless, of course, you're keeping the number/line live in permanence? But I can't see how your service would make that work financially.

If you re-read what I wrote, or perhaps quote the whole thing, you'll see that I was referring to the SIM, not to the phone number.

Of course unless phone numbers perpetually get longer, they have to eventually get re-used. We don't implement any re-use but the operator will indeed eventually recycle them.

Great to know that the SIM numbers are not re-used across customers. Would this also mean that I have no way to re-claim a previously owned number?

You can keep a phone number as long as you like. If you accidentally delete it or allow it to expire, then we can probably, on a best-effort basis, recover the phone number for you if you alert us quickly after you make the mistake. Once we have done a resupply of the SIM card pool the SIMs that have been used and are no longer in use are destroyed, at which point we can't get the number back for you.

The monthly charges seem reasonable. I didn't see any info on the site about inbound call pricing, service and limitations. Specifically:

- per-minute charges?

- # simultaneous channels?

- delivery options? (e.g. can I register a SIP device on your gateway, or can you accept a SIP URI)

Thanks - we'll add this information.

The per-minute charges are fixed for a given number type for inbound calls. They're cheapest for landline numbers (e.g. just under EUR 0.01 per minute for a UK landline), very slightly more expensive for mobile numbers, and quite a lot more expensive for toll-free numbers (since you're paying the cost for the caller). For outbound calls, it depends where you're calling. There are volume discounts available.

We guarantee one simultaneous channel per phone number for Basic accounts. For Pro accounts ($10/month) we guarantee an additional 8 simultaneous channels which can be used across any of the phone numbers as demand requires. Those are guarantees and our system will often allow bursting above them if capacity allows.

For Business accounts (negotiated minimum spend) we can negotiate any number of simultaneous channels.

Pro & Business accounts have SIP support, both registration and directing inbound calls to a SIP URI.

Thanks for the clarification. It makes sense. Not having that info available might discourage some people from signing up, but of course you should test it :)

Your service seems similar to DIDLogic, except that:

- there's no monthly minimum spend

- you're explicitly open to small users and short term users (not just corporates and telcos)

- you offer SMS (not just voice)

The product looks nice.

Any one have any idea how to get numbers of any kind (VoIP is fine) that can send and receive SMS from a country like Slovenia? Big providers like Twilio don’t provide it. Twilio only provides sending. Thanks for any help.

The product offering of a per-hour mobile number to receive SMS is great, I've not seen this elsewhere.

Do you have any concrete plans to expand the SIM mobile number service beyond the UK?

It requires infrastructure, so it's not trivial, but we're investigating some options. Obviously it would only be practical in other countries that don't require SIM registration, or if they do, it needs to be possible to do it via some kind of API or other reasonably automated means so that we can build a system to let people register their SIMs.

How does this work? Is there an app?

You rent a virtual mobile, landline or toll-free phone number, or a physical SIM, via the website or Android app. The phone number is then yours as long as you keep paying the rental fee. (After you delete it or stop paying, we don't give it to anyone else - we return the number to the upstream phone networks who will, as with all phone numbers, 'quarantine' it for many months and then eventually re-use it.)

You can then send and receive SMS, make and receive calls and send faxes using the numbers via the website or the Android app.

Pro accounts can also make and receive calls via SIP.

Any plans for an iPhone app?

The app actually supports iOS already (it's built with Flutter) but we changed legal entity and made a mistake with the app transfer process, so it's temporarily unavailable. We're hoping to have it back on the store in the next week or so.

No toll free in Chile :(

Sorry! We're always adding new number types and countries though, so keep an eye.

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