[Serusers] How to redirect pstn calls to another server?

Hi, I've setup ser ser-0.8.14 on Red Hat Linux 9.0. I've successfully configure to enable SIP phone calling to other SIP Phone. I'm having an account with simpletelecom.com to call from SIP to PSTN lines. Is there any way that I can redirect all the PSTN calls from ser to simpletelecom.com? I tried with rewritehost or rewritehostport, but simpletelecom required a username and password for authentication, is there any way that I can pass a username and password from ser to another server? I'm having 20 users on ser, and I would like all the users to use the same account on simpletelecom to call out to PSTN. You help is greatly appreciated. Thank you. Best Regards KH Ch'ng keehiang(a)platronix.com