I have been using the Piranha Sim for a few months now, i have been on business in the US,Canada, Australia, Germany, Singapore,Thailand and South Africa. So far it has worked without issue, I am UK based and i have tested there without issue, i have found that there support is very quick to answer any questions and i did receive my Sim card within 2 days of order, so all in all quite happy. I would not know about Telna sorry, hope this helps and Merry Xmas.

Who/What is Telna??
 

I think that Telna is a little unique and strange in this business. Not neccesarily a bad thing. It actually owns some infrastructure/tower[s]/frequency licences in the USA. I do not know where or how much. It does allow them a bit more flexibility in making deals with other companies.
In the USA, Piranha uses Telna and T-Mobile for carriers. Until someone actually reports seeing 'Telna' as thie network on their cellphone, I would assume 99.9% of the time will be on T-Mobile in the USA. I assume that Piranha uses Telna to get access to the T-Mobile network. Probably much easier than dealing with T-Mobile itself.

This is my understanding, but not verified in any way to be true. Thus, if anyone _knows_ with more certainty than idle speculation, I would love to stand corrected.

If you go to:::Mobile World Live - Coverage Maps

And then scroll down and click on United States and then scroll down to:
>>Telecom North America Mobile Inc. (telna Mobile)
You will see about all there seems to be available about Telna.

Here is some more from Telna's website.

So there you have it. Somewhere in Missouri they have a network. So if anyone happens to be in Missouri with a Piranha SIM, watch your phone.
I know of no links between Telna and Piranha other than this network use.

El Dorado Springs, MO 64744
 

El Dorado Springs, MO 64744

Area code 417 prefix 400 is the only prefix for TELECOM NORTH AMERICA MOBILE in the USA [as best as I can tell]. That is where they are a cell provider.

The FCC licensee database shows three PCS (1900 MHz) licenses for Telecom North America: St. Louis, MO; Flagstaff & Prescott, AZ. They appear to lease spectrum from Commnet in MO and to them in AZ.

Commnet
 

This keeps getting better.
I was able to find six prefixes for Commnet in Arizona.
Tucson in the 520 area code.

928 area code: PAGE, TUBA CITY, DILKON, KAYENTA, FT DEFIANCE.
These in the 928 service near or in the Navajo Nation [also possibly the Hopi Nation. Page is outside of the Navajo Nation but on former land of the Navajo.
All these prefixes serve small communities and one prefix is enough for them. Also, there are probably other cell providers in each.
Coverage maps: Commnet Wireless

what is actually the use of these very tiny mobile operators in the US that cover one or two corn fields? Is that more like a network for closed communication (like a petrol company or sth like that) or do they really seriously getting customers?

Mostly they are purchased like land to resell. Sometimes the theory is to make money from roaming revenues. Occasionally it is a small town that just wants service and the big guys didn't think it was worth it.

Remember that the US started with a bunch of these companies and they were bought out. We did not do like most of the EU and grant licenses nationally. The theory at the outset was that the smaller licenses holders would have a greater incentive to cover their little plot of coverage area. Until roughly 2000, most Americans had plans like the folks in Canada, Mexico, and India do where we roamed if we got 80k from our homes.

Notice that Verizon Wireless holds a number of GSM licenses in the US even though they use the competing CDMA technology. In small towns where they have licenses, they will often through up "roamer nets" which are GSM networks solely designed to get roaming revenues from GSM visitors who travel through or visit these towns.

The United States is geographically as large as the EU but when you get away from the coasts, we have a large areas of land with very light population density. There is an opportunity for investors to develop this areas for roaming revenues and eventually to sell to the big guys. Additionally, several years ago our Justice Department granted an antitrust waiver to the major U.S. carriers to develop roaming collectives for desolate parts of our country. ATT, Sprint, Verizon, and TMobile can agree to jointly cover a desolate stretch of a North Dakota freeway and each invest in the collective. Lastly, a small amount of the US carriers are actually Indian Tribal Governments who function as semi-autonomous/self-governing regions in the US. In addition to raising revenues from roamers, they may have an aspect demonstrating self-autonomy over practicality.

I was looking at the Canadian list of small providers last night and there were a lot of tiny Canadian ones I never heard of. The idea of buying one of these to take advantage of Government mandated lower roaming rates is interesting. E.g. China Mobile buying the Artic GSM cooperative outside of Anchorage and letting China Mobile subscribers get FCC mandated domestic discounted roaming rates.

During my trip to South Korea and the Piranha SIM worked good. The first time the SIM needs to register in a new network takes really long. Round about 30 minutes in South Korea. Back in Germany the SIM needed round about 12 hours to register in a network. During this time I have tried to register with different mobiles.

Does anybody knows what the reason for this is?

The Callback worked really good and the voice quality was also high.

Sometimes I was not direct reachable over the US number. The caller had to try 3 or 4 times to reach me.

The VOIP application worked for outgoing calls good with also a good voice quality. For incoming calls was the voice quality was really bad and I removed the VOIP application from my phone.

SMS are only working outgoing. I' am not getting any incoming SMS. Only the SMS from the Piranha support are working.

The prices are really good and I hope Pirnaha will be longer in business.

SMS issues?
 

I have been testing [playing with] the SIM. I do get SMS sent to my US number. I did not get SMS to my UK number. This was from a US AT&T MVNO and a Philippine SMART SIM. This was done from California.
Sending an SMS from Piranha's web site worked for both the US and UK numbers.