partner-contact/partner_phone_extension/res_partner_view.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
  <data>

    <!-- Add phone number extension fields for partner -->
    <record id="view_partner_simple_number_extension_form" model="ir.ui.view">
    <field name="name">view.partner.simple.number.extension.form</field>
    <field name="model">res.partner</field>
    <field name="inherit_id" ref="base.view_partner_simple_form"/>
    <field name="arch" type="xml">

      <field name="phone" position="after">
        <field name="extension"/>
      </field>

    </field>
    </record>

    <record id="view_partner_number_extension_form" model="ir.ui.view">
      <field name="name">view.partner.number.extension.form</field>
      <field name="model">res.partner</field>
      <field name="inherit_id" ref="base.view_partner_form"/>
      <field name="arch" type="xml">

        <field name="phone" position="after">
           <field name="extension"/>
        </field>

        <xpath expr="//form[@string='Contact']//field[@name='phone']"
               position="after">
          <field name="extension"/>
        </xpath>

      </field>
    </record>

  </data>
</openerp>