Rustu Kaya wrote:
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To meet the TELCO`s standarts from the line perspective is piece of cake indeed. Even the simplest form of circuit (as I described earlier) can easily meets the specs with some minor modifications.

A piece of cake? "Easily"? "minor modifications"?

Have you ever actually designed a telephone line interface that has been type-approved? I seriously doubt it, reading the above.

But the the problem is how you are going to convince the TELCO authorities.

The only way to convince them is to make sure your product complies with the appropriate standards.

If you are not going to a commertial production in a volume, it is not worthwhile to take such a challange

Worthwile has got nothing to do with it! As both Andy and myself have already said several times: Selling a device that does not comply with the regulatory standards is illegal and can get you into serious trouble! No matter if you sell one or one hundred thousand items, you, the manufacturer, are responsible for the correct operation of your device.

Rob.