TRAI according to this official document has asked all the telecom operators to treat an SMS sent to 1900 as any other normal SMS and not as special SMS which are generally charged 5 or 6 Rupees. The total cost to switch using MNP should not be more than 19 and if a subscriber is charged so high, the total cost of MNP increases by 40% at least.
It says :
Now therefore, in exercise of powers conferred upon the Telecom Regulatory Authority of India under section 13, read with clause (b) of subsection (1) and sub-section (2) of section 11 of the Telecom Regulatory Authority of India Act, 1997 (24 of 1997), and in order to protect interests of the consumers of telecom sector and to facilitate growth of telecom services in India and for the reasons mentioned in the preceding paragraphs, the Telecom Regulatory Authority of India hereby directs the Cellular Mobile Telephone Service Providers and Unified Access Service Providers to treat the SMS sent to short code number 1900 as ordinary SMS for the purpose
Related : Steps for changing your Mobile Operator [ MNP ]