Q: With iPhone 4 iOS 7 I can't make conference call? Any suggestion

Hi kushalfromct,

Welcome to the Support Communities!

The article below may be able to help you with this.

Click on the link to see more details and screenshots. 

iPhone: Understanding phone features

http://support.apple.com/kb/ht4515

GSM networks support of to five calls simultaneously.

CDMA networks support up to two calls simulatneously.

Make a conference call - Phone - iPhone Basics - Apple Support

http://support.apple.com/kb/TI12#TI12

iOS: Understanding cellular data networks

http://support.apple.com/kb/HT1976

Cheers,

- Judy