Hi there and welcome
With the standard stock App you cannot get around this. For some reason they changed how this works, but there are workarounds for it
The first, get Handcent SMS. It is a full featured texting app that is free on the Market and will give you the + symbol back in the To: ***** ***** you access to the Contact list.
Else you can get an app called DW Contact Group Manager. It will allow you to send a text to multiple recipients by selecting them from your contacts list.
You need to use one of these two apps on this phone to get around it.
Personally I recommend Handcent SMS as it is more functional.
If you would like any additional information or assistance, please do not hesitate to let me know.
Else if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.