There's been a huge problem recently with the Android Operating System and it not sending text messages to the contact you intend to send it to, but it seems Google have released an update that fixes this problem.
Both the Nexus One and its successor the Nexus S have faced this problem. Now they've both got updates that take their operating system version to the 2.2.2 and 2.3.2, Froyo and Gingerbread, versions of Android respectively. The updates are expected to roll out very soon.
Now you don't have to worry about the texts to your signifact other reaching the mobile phone of your mother anymore.