I also don't see anything wrong with your setup, but there is another way to fork calls to a cell phone and it might be a better way. The way you're doing it, your cell phone will not receive the correct CallerID. It will receive the SP1 phone number as CallerID.
Your Cell Phone must be a Smart Phone.
Get a free SIP account at Callcentric or Sip2Sip.
Install a softphone on your cell.
Register the softphone to the SIP account.
OBi InboundCallRoute:
{ph1,spx(17771234567@in.callcentric.com;ui=$1)}
or
{ph1,spx(your_account_id@sip2sip.info;ui=$1)}
spx must be defined as SIP
ui is userid
$1 is an OBi variable containing the inbound callerid