Laws and regulations regarding routing calls to/from VOIP to PSTN vary country to country. For example in Germany you can do whatever you want in terms of call routing as long as you do not alter any user's chosen privacy settings (CLI hiding etc.), spam or harass anyone. In some countries like U.K, U.S.A, Netherlands, Australia etc. if you are planning to start a service then you may also be required to have legal interception capability.
In India, you can not mix VOIP and PSTN call beyond your own network, and you need a license to do so.
In Pakistan, VOIP is completely ban, so you can not run a VOIP setup at all without any license. Even with license you are not allowed to route national calls to international destinations or international calls to national destination without explicit permission from Pakistan Telecom Authority.
These are general guidelines, for exact information contact your national telecom authority.
Thank you.
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Mit freundlichen Grüßen
Muhammad Shahzad
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CISCO Rich Media Communication Specialist (CRMCS)
CISCO Certified Network Associate (CCNA)
Cell: +49 176 99 83 10 85
MSN: shari_786pk@hotmail.com
Email: shaheryarkh@googlemail.com