Sip Question 3G or 4G service

[giga]

Is the sip library only functional over a WIFI connection or can it be used over 3G/4G?
I had it working before and now it just stopped and not working out of the office(WIFI).

 

[Erel]

Seems like some device manufacturers limit its usage: google - Why does the native SIP stack included in Android 2.3 does not work over 3g? - Stack Overflow