IP Connection to Phone Number

Yes, but only through circuit switched data (CSD) which would be billed by time as opposed to volume and bandwidth would be very limited (14.4 KBit/s on GSM an 64 KBit/s on UMTS). Also none of the current operating systems supports such dial-up mode out of the box and I even doubt that there are APIs to access CSD connectivity as this is outdated technology.

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Original geschrieben von Blackcoat
Thanks for the quick answer.
- Is it correct, that the package oriented data services GPRS, EDGE, UMTS and HSDPA cannot be used to connect two smartphones (except using CSD)?

Maybe it is possible on TCP/IP level if

* both handsets are connected to the same network provider
* at least one (network internal) IP address is known
* and the network provider does not block incoming TCP traffic which does not use an already opened connection.

The last part should be the one where the idea dies.

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- Is the data for CSD modulated by a modem like on analog telephone lines?

No, due to the fact, that GSM is a digital protocol, there is no need to convert the data to "audio" signals

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- Why is the maximum speed that much limited?

The usable data bandwidth of a single GSM canal is 9.6kbit/s, under good radio circumstances you can use a 14.4kbis/s encoding, but that is not as robust against errors as the slower encoding. Using fixed line modem encodings would not work due to the fact, that the audio codecs are specialized to speech signals and would destroy the encoded data. The standard full rate speech codec has a bandwidth of 13 kbit/s, so a 56.7kbit/s modem connection would be heavily scrambled and the transcoding steps from digital via analog via digital via analog to digital do not help either.

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Original geschrieben von Blackcoat
- Is it correct, that the package oriented data services GPRS, EDGE, UMTS and HSDPA cannot be used to connect two smartphones (except using CSD)?

No. You can connect two smartphones but you need to overcome firewalls and NAT which most MNOs use. A reliable method is STUN .

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- Is the data for CSD modulated by a modem like on analog telephone lines?

No. As el_emka said it's fully digital.

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- Why is the maximum speed that much limited?

Because CSD connections on UMTS were specified long time ago when UMTS was limited to 384 KBit/s. Further CSD by definition requires a certain amount of bandwidth to be permanently dedicated to the subscriber, even if no data is transfered. This wastes a lot of capacity and would mean very few users establishing such high-speed CSD connections would eat up all capacity on the local cell. Packet-oriented data is much more efficient here as it makes significantly better use of capacity and allows it to be equally distributed among users.