Some time ago, we bought new SIP GSM gateway for our PBX. The GSM gw is BlueGate sip GSM gateway, dual SIM (http://www.alphatechtechnologies.cz/en/products/gsm-gateways/voip-gsm-gateway-bluegate-sip/).
I read in the spec that it is coming with Siemens radio module and decided that the GW will be made with high quality in mind.
Unfortunately this was not the case and we faced our firs issue.
The operators started complaining that they hear noise during call, and despite the fact that the signal to noise ratio is very good, the noise which is heard during call is too loud and very very annoying.
The noise is coming from the radio module and the producer of the GW confirmed it, but they said that they will not do anything about it. Here is their last answer from the communication with them:
I haven't good news. I got the BG SIP twin yesterday. I tested
it with our specialist for analog signals. The moment BG SIP twin
connect analog output from GSM modul we hear the noise from the
GSM modul too. But we can't take out only noice incomming from GSM
modul. I do nothing with it.
Until now we used Vierling GSM GW which was using ISDN to connect with PBX and we have had no problem with it, but I decided to switch to SIP and bought the crap described above.
The second issue we have had with this device, is that probably in 99% of the cases, it was not passing DTMF tones to the PBX. We just did not get any DTMF and the clients which were calling us on these lines were not able to choose anything from the IVR menu.
Considering the issues with the noise, we did not even bothered to write again to their support, because we already knew that this device is dead for us.
As a conclusion: DO NOT buy BlueGate SIP GSM gateway from http://www.alphatechtechnologies.cz. They suck.
Now we have direct land line SIP trunk with the mobile operator, and all is just fine.